Electrical investigation of p-type 4H-SiC heavily doped by ion implantation

In the last decades, an increasing interest in the research field of wide bandgap semiconductors was observed, mostly due to the progressive approaching of silicon-based devices to their theoretical limits. 4H-SiC is an example among these, and is a mature compound for applications. The main advantages offered 4H-SiC in comparison with silicon are an higher breakdown field, an higher thermal conductivity, a higher operating temperature, very high hardness and melting point, biocompatibility, but also low switching losses in high frequencies applications and lower on-resistances in unipolar devices. Then, 4H-SiC power devices offer great performance improvement; moreover, they can work in hostile environments where silicon power devices cannot function. Ion implantation technology is a key process in the fabrication of almost all kinds of SiC devices, owing to the advantage of a spatially selective doping. This work is dedicated to the electrical investigation of several differently-processed 4H-SiC ion- implanted samples, mainly through Hall effect and space charge spectroscopy experiments. It was also developed the automatic control (Labview) of several experiments. In the work, the effectiveness of high temperature post-implant thermal treatments (up to 2000°C) were studied and compared considering: (i) different methods, (ii) different temperatures and (iii) different duration of the annealing process. Preliminary p + /n and Schottky junctions were also investigated as simple test devices. 1) Heavy doping by ion implantation of single off-axis 4H-SiC layers The electrical investigation is one of the most important characterization of ion-implanted samples, which must be submitted to mandatory post-implant thermal treatment in order to both (i) recover the lattice after ion bombardment, and (ii) address the implanted impurities into lattice sites so that they can effectively act as dopants. Electrical investigation can give fundamental information on the efficiency of the electrical impurity activation. To understand the results of the research it should be noted that: (a) To realize good ohmic contacts it is necessary to obtain spatially defined highly doped regions, which must have conductivity as low as possible. (b) It has been shown that the electrical activation efficiency and the electrical conductivity increase with the annealing temperature increasing. (c) To maximize the layer conductivity, temperatures around 1700°C are generally used and implantation density high till to 10 21 cm -3 . In this work, an original approach, different from (c), is explored by the using very high annealing temperature, around 2000°C, on samples of Al + -implant concentration of the order of 10 20 cm -3 . Several Al + -implanted 4H-SiC samples, resulting of p-type conductivity, were investigated, with a nominal density varying in the range of about 1-5∙10 20 cm -3 and subjected to two different high temperature thermal treatments. One annealing method uses a radiofrequency heated furnace till to 1950°C (Conventional Annealing, CA), the other exploits a microwave field, providing a fast heating rate up to 2000°C (Micro-Wave Annealing, MWA). In this contest, mainly ion implanted p-type samples were investigated, both off-axis and on-axis <0001> semi-insulating 4H-SiC. Concerning p-type off-axis samples, a high electrical activation of implanted Al (50-70%) and a compensation ratio below 10% were estimated. In the work, the main sample processing parameters have been varied, as the implant temperature, CA annealing duration, and heating/cooling rates, and the best values assessed. MWA method leads to higher hole density and lower mobility than CA in equivalent ion implanted layers, resulting in lower resistivity, probably related to the 50°C higher annealing temperature. An optimal duration of the CA treatment was estimated in about 12-13 minutes. A RT resistivity on the lowest reported in literature for this kind of samples, has been obtained. 2) Low resistivity data: variable range hopping Notwithstanding the heavy p-type doping levels, the carrier density remained less than the critical one required for a semiconductor to metal transition. However, the high carrier densities obtained was enough to trigger a low temperature impurity band (IB) conduction. In the heaviest doped samples, such a conduction mechanism persists till to RT, without significantly prejudice the mobility values. This feature can have an interesting technological fall, because it guarantee a nearly temperature- independent carrier density, it being not affected by freeze-out effects. The usual transport mechanism occurring in the IB conduction is the nearest neighbor hopping: such a regime is effectively consistent with the resistivity temperature behavior of the lowest doped samples. In the heavier doped samples, however, a trend of the resistivity data compatible with a variable range hopping (VRH) conduction has been pointed out, here highlighted for the first time in p-type 4H-SiC. Even more: in the heaviest doped samples, and in particular, in those annealed by MWA, the temperature dependence of the resistivity data is consistent with a reduced dimensionality (2D) of the VRH conduction. In these samples, TEM investigation pointed out faulted dislocation loops in the basal plane, whose average spacing along the c-axis is comparable with the optimal length of the hops in the VRH transport. This result suggested the assignment of such a peculiar behavior to a kind of spatial confinement into a plane of the carrier hops. 3) Test device the p + -n junction In the last part of the work, the electrical properties of 4H-SiC diodes were also studied. In this case, a heavy Al + ion implantation was realized on n-type epilayers, according to the technological process applied for final devices. Good rectification properties was shown from these preliminary devices in their current-voltage characteristics. Admittance spectroscopy and deep level transient spectroscopy measurements showed the presence of electrically active defects other than the dopants ones, induced in the active region of the diodes by ion implantation. A critical comparison with the literature of these defects was performed. Preliminary to such an investigation, it was assessed the experimental set up for the admittance spectroscopy and current-voltage investigation and the automatic control of these measurements.

Origine de la réduction de la durée de vie des photoporteurs dans le InGaAsP implanté à basse température

Un matériau semi-conducteur utilisé lors de la fabrication d’antennes térahertz (THz), le quaternaire InGaAsP (E_g = 0,79 eV), subit une implantation ionique de Fe suivi d’un recuit thermique rapide (RTA) dans le but d’améliorer ses propriétés d’émission. Le recuit est nécessaire afin de recristalliser la couche amorphisée lors de l’implantation, donnant lieu à un polycristal rempli de défauts de recristallisation. On constate cependant que les matériaux implantés Fe offrent de meilleures performances que ceux simplement endommagés au Ga. Dans le but de départager l’effet des défauts de recristallisation et des impuretés de Fe, des mesures de spectroscopie transitoire des niveaux profonds (DLTS) et de DLTS en courant (I-DLTS), ainsi que de spectrométrie de masse d’ions secondaires par temps de vol (ToF-SIMS) ont été effectuées sur des échantillons non implantés et d’autres recristallisés. Les mesures DLTS et I-DLTS ont pour but de caractériser les niveaux profonds générés par ces deux procédures postcroissance, tout en identifiant le rôle que jouent les impuretés de Fe sur la formation de ces niveaux profonds. De plus, le voisinage des atomes de Fe dans le matériau recristallisé a été étudié à l’aide des mesures ToF-SIMS. Les mesures DLTS sur matériau recristallisé sont peu concluantes, car la mesure de capacité est faussée par la haute résistivité du matériau. Par contre, les mesures I-DLTS sur matériau recristallisé ont permis de conclure que les impuretés de Fe sont responsables de la formation d’une grande variété de niveaux d’énergie se trouvant entre 0,25 et 0,40 eV, alors que les défauts de structure induisent des niveaux de moins de 0,25 eV. La concentration de Fe est élevée par rapport au seuil de solubilité du Fe dans le matériau recristallisé. Il serait donc plausible que des agrégats de Fe se forment. Toutefois, cette hypothèse est infirmée par l'absence de pic aux masses correspondant à la molécule ^(56)Fe_2^+ sur les spectres ToF-SIMS. De plus, un modèle simple est utilisé afin d’estimer si certaines masses présentes sur les spectres ToF-SIMS correspondent à des liaisons non induites par la mesure dans le matériau recristallisé. Bien qu’aucune liaison avec le Ga et l'As n’est détectable, ce modèle n’exclut pas la possibilité de liens préférentiels avec l’In.

Origine de la réduction de la durée de vie des photoporteurs dans le InGaAsP implanté à basse température

Un matériau semi-conducteur utilisé lors de la fabrication d’antennes térahertz (THz), le quaternaire InGaAsP (E_g = 0,79 eV), subit une implantation ionique de Fe suivi d’un recuit thermique rapide (RTA) dans le but d’améliorer ses propriétés d’émission. Le recuit est nécessaire afin de recristalliser la couche amorphisée lors de l’implantation, donnant lieu à un polycristal rempli de défauts de recristallisation. On constate cependant que les matériaux implantés Fe offrent de meilleures performances que ceux simplement endommagés au Ga. Dans le but de départager l’effet des défauts de recristallisation et des impuretés de Fe, des mesures de spectroscopie transitoire des niveaux profonds (DLTS) et de DLTS en courant (I-DLTS), ainsi que de spectrométrie de masse d’ions secondaires par temps de vol (ToF-SIMS) ont été effectuées sur des échantillons non implantés et d’autres recristallisés. Les mesures DLTS et I-DLTS ont pour but de caractériser les niveaux profonds générés par ces deux procédures postcroissance, tout en identifiant le rôle que jouent les impuretés de Fe sur la formation de ces niveaux profonds. De plus, le voisinage des atomes de Fe dans le matériau recristallisé a été étudié à l’aide des mesures ToF-SIMS. Les mesures DLTS sur matériau recristallisé sont peu concluantes, car la mesure de capacité est faussée par la haute résistivité du matériau. Par contre, les mesures I-DLTS sur matériau recristallisé ont permis de conclure que les impuretés de Fe sont responsables de la formation d’une grande variété de niveaux d’énergie se trouvant entre 0,25 et 0,40 eV, alors que les défauts de structure induisent des niveaux de moins de 0,25 eV. La concentration de Fe est élevée par rapport au seuil de solubilité du Fe dans le matériau recristallisé. Il serait donc plausible que des agrégats de Fe se forment. Toutefois, cette hypothèse est infirmée par l'absence de pic aux masses correspondant à la molécule ^(56)Fe_2^+ sur les spectres ToF-SIMS. De plus, un modèle simple est utilisé afin d’estimer si certaines masses présentes sur les spectres ToF-SIMS correspondent à des liaisons non induites par la mesure dans le matériau recristallisé. Bien qu’aucune liaison avec le Ga et l'As n’est détectable, ce modèle n’exclut pas la possibilité de liens préférentiels avec l’In.

Conflict and communication among engineers

The trend of cultural diversity is increasing in all organizations, especially engineering ones, due to globalization, mergers, joint ventures and the movement of the workforce. The collaborative nature of projects in engineering industries requires long-term teamwork between local and international engineers. Research confirms a specific culture among engineering companies that isassumed to have a negative effect on collaboration and communication among co-workers. Multicultural workplaces have been reported as challenging environments in the engineering work culture, which calls for more research among engineering organizations. An everyday challenge for co-workers, especially in culturally diverse contexts, is handling interpersonal conflict. This perceived conflict among individuals can happen because of actual differences in tasks or relationships. Research demonstrates that task conflict at the group level has some positive effects on decision-making and innovation, while it has negative effects on employees’ work attitude and performance. However, relationship conflict at the individual level has only negative effects including frustration, tension, low job satisfaction, high employee turnover and low productivity. Outcomes of both task and relationship conflict at individual level can have long-term negative consequences like damaged organizational commitment. One of the most important sources of differences between individuals, which results in conflict, is their cultural backgrounds. First, this thesis suggests that in culturally diverse workplaces, people perceive more relationship conflict than task conflict. Second, this thesis examines interpersonal communication in culturally diverse work places. Communicating effectively in culturally diverse workplaces is crucial for today’s business. Culture has a large effect on the ways that people communicate with each other. Ineffective communication can escalate interpersonal conflict and cause frustration in the long term. Communication satisfaction, defined as enjoying the communication and feeling that the communication was appropriate and effective, has a positive effect on individuals’ psychological wellbeing. In a culturally diverse workplace, it is assumed that individuals feel less satisfied with their interpersonal communications because of their lack of knowledge about other cultures’ communication norms. To manage interpersonal interactions, many authors suggest that individuals need a specific capability, i.e., cultural intelligence (some studies use cultural competence, global intelligence or intercultural competence interchangeably). Some authors argue that cultures are synergic and convergent and the postmodernist definition of culture is just our dominant beliefs. However, other authors suggest that cultural intelligence is the strongest and most comprehensive competency for managing cross-cultural interactions, because various cultures differ so greatly at the micro level. This thesis argues that individuals with a high level of cultural intelligence perceive less interpersonal conflict and more satisfaction with their interpersonal communication. Third, this thesis also looks at individuals' perception of cultural diversity. It is suggested that level of cultural diversity plays a moderating role on all of the proposed relationships (effect of cultural intelligence on perception of relationship conflict/ communication satisfaction) This thesis examines the relationship among cultural diversity, cultural intelligence, interpersonal conflict and communication by surveying eleven companies in the oil and gas industry. The multicultural nature of companies within the oil and gas industry and the characteristics of engineering culture call for more in-depth research on interpersonal interactions. A total of 286 invitation emails were sent and 118 respondents replied to the survey, giving a 41.26 per cent response rate. All the respondents were engineers, engineering managers or practical technicians. The average age of the participants was 36.93 years and 58.82 per cent were male. Overall, 47.6 per cent of the respondents had at least a master’s degree. Totally, 42.85 per cent of the respondents were working in a country that was not their country of birth. The overall findings reveal that cultural diversity and cultural intelligence significantly influence interpersonal conflict and communication satisfaction. Further, this thesis also finds that cultural intelligence is an effective competency for dealing with the perception of interpersonal relationship conflict and communication satisfaction when the level of cultural diversity is moderate to high. This thesis suggests that cultural intelligence training is necessary to increase the level of this competency among employees in order to help them to have better understanding of other cultures. Human resource management can design these training courses with consideration for the level of cultural diversity within the organization.

Meän tapa puhua : Tornionlaakso pellolaisnuorten subjektiivisena paikkana ja murrealueena

This folk linguistic and human geographic study deals with dialect awareness, dialect use and place attachment. The study discusses theoretical and methodological issues current in sociolinguistics suggesting that the study of attitudes should be regarded as a core area in the study of variation and change. Furthermore, it is suggested that instead of putting effort into improving mental mapping methodology (adopted into folk linguistics from behavioural geography of the 1960 s), the more up-to-date thinking of space in geography should be adopted. The region and the dialect are treated as perceptual constructs in the study. The dialect perceptions of high school seniors in the Finnish Tornio Valley are examined trough a triangulation method involving a questionnaire, interviews and dialect recognition test as the research methods. The h in non-initial syllables (e.g. lähethä(ä)n, saunhaan ~ sauhnaan let s go into sauna ) turns out, expectedly, as the most salient feature in the dialect awareness of the locals and in terms of local identity construction. This feature is no longer heard in most of the present dialects of Finnish but is still thriving in the Tornio Valley in the cross-border dialect area. The metathetic variant (saunhaan > sauhnaan into sauna , käymhään > käyhmään to go ) is a characteristic feature of the Tornio Valley dialect. However, individual differences have long been found in the use of the h. This study challenges the essentialist variationist view of social categories (gender) by analysing variation from a quantitative but emic and human geographic point of view. The study shows that the variation of the h is statistically significantly patterned in terms of the degree of feeling of insideness vs. outsideness. New light is shed on the gender differences found in earlier sociolinguistic studies: differences in dialect use between and inside gender groups are illuminated by the fact that, in this case, it is young women who are generally less attached to the local community than young men, but this does not hold for all the individuals. The ideological motivation for preservation of the h seems to be based on the imagined community of Tornio Valley covering both the Swedish and the Finnish valley area. The general image of the dialect area and it s speakers, the shared cognitive dialect boundaries of the locals and the particularly deep level of awaress of the linguistic variation of the h are notable resources of the Tornio valley identity. Hyperdialectic forms analogical to the most frequently attested metathetic forms are found in the interview data, predicting that in this dialect the h will be maintained also in the future.

Kaaoksen kautta tai hitaasti kiiruhtaen : Pedagoginen muutosprosessi luokanopettajan näkökulmasta

The purpose of this study was to describe and get a deep understanding of pedagogical change process. The phases of pedagogical change process and the nature and the role of teacher s pedagogical thinking in it were mapped. The change process as a whole was also modeled. The previous research of teaching change process has had been scarce on an individual teacher level, but on a school level it has been investigated abundantly. The theoretical background of this study consists of theories of teacher s pedagogical thinking and action and how their thinking and action change and develop. Teacher change has been researched from the point of view of both school change and professional development. The basic principle in the theoretical frame is that change in teacher s thinking leads to change in action. Three men teachers and a woman teacher who have put change into practice took part in this study. The data consisted of two parts: teachers essays of their change process and interviews that were based on the essays. The data was analysed by content analysis. The categorizations of both parts of the data were made separately but they were interpreted together. In this way a deep understanding of pedagogical change process could be reached. The results of this study were descriptions of the phases of pedagogical change process and the nature and the role of teacher s pedagogical thinking in it. In addition a model of pedagogical change process was presented. Pedagogical change process started up because of disorder in teacher s pedagogical thinking and action. The disorder leads to an absolute necessity to change the activities. Change activities stabilize throughout intuitive experiments and reflection-on-action. The change in a teacher s thinking is a prerequisite for the start of the process but also, a teacher s thinking develops as a result of the process. Thus, the whole process results in a real, deep level change in instruction and in the teacher s thinking. That is why pedagogical change processes are visible, significant and they have wide and extensive effects. The study gives out information of controlling the change processes. Consequently, the results of this study encourage teachers to confront change and put their new ideas into practice. Keywords change, development, pedagogical thinking, pedagogical action, teaching-studying-learning process

Herrat, jätkät ja sotataito : Kansalaissotilas- ja ammattisotilasarmeijan rakentuminen 1920- ja 1930-luvulla

Gentlemen, Lads and the Art of War The Construction of Citizen Soldier- and Professional Soldier Armies into the Miracle of the Winter War During the 1920s and 1930s The Miracle of the Winter War was not a myth - at least according to them, who were making that miracle to happen. This study is not just about the Armed Forces and society, but moreover a study about civil society inside the organization of armed forces. Conscription kept Finnish military organization (and is still keeping) very closely connected with civil society and therefore there is no need to locate the possible critical misunderstandings brought by two different identity-based approaches. The great performance of the Armed Forces during the Second World War was not made of superior art of war. It was not the high level of discipline either. Art of war is basically a (deep level) cultural level equation that has more to do with culturally absorbed schemes of meaning making than rational decision-making. Naturally attrition based approach to effect-making directed the organizational methods in attrition based organisational practices, where there were only minor possibilities to practice any manoeuvre-based organisational behaviour. The practice and method of leadership lent similarly to the attrition-based thinking, which directed the organisational cultural thoughts towards composition that confirmed antagonism between gentlemen and lads . This setting has been absorbed and learned through cultural socialisation and was therefore not a product of the military organisation itself. The Finnish Armed Forces included two different communities (gentlemen and lads) within the same organisation as there were both the official and the unofficial organisations presented. This caused problems as they both made meaning-making processes simultaneously. These organisations had their own overlapping and in most cases also contradictory social meanings. The unofficial organisation has been overshadowed by the vast number of studies concerning the official organisation. The main reason for this systematic neglect is based on the reality of the attitudes and living conditions of the micro-level organisation which produced (perhaps) too realistic and repulsive viewpoints that are presenting a picture of a national level identity process in a way that is separating it from the ideals made to verify the ethos of national values. Complaining, griping, grumbling and moaning are usually situated in a category of abnormal and unwanted behaviour. However, within the context of a citizen soldier army community this was more of a characteristic feature of that organisation (in Finland) and therefore it was crucially important to locate the context of that abnormal behaviour. According to this study, it was not a malicious act but moreover seriously formed efforts in trying to use common sense in the chaos citizen soldiers faced when they were uniformed and placed in an unfamiliar process of disciplinary measures and frictions and competition between different ranks. There is much evidence that reinforces the argument that what seemed to be the most unconventional behaviour was finally the most efficient in a sense of military performance.

Interface states of laser ablated BaTiO3 and Ba0.9Ca0.1TiO3 thin films in MFS structure determined by DLTS and C – V technique

BaTiO3 and Ba0.9Ca0.1TiO3 thin films were deposited on the p – type Si substrate by pulsed excimer laser ablation technique. The Capacitance – Voltage (C-V) measurement measured at 1 MHz exhibited a clockwise rotating hysteresis loop with a wide memory window for the Metal – Ferroelectric – Semiconductor (MFS) capacitor confirming the ferroelectric nature. The low frequency C – V measurements exhibited the response of the minority carriers in the inversion region while at 1 MHz the C – V is of a high frequency type with minimum capacitance in the inversion region. The interface states of both the MFS structures were calculated from the Castagne – Vaipaille method (High – low frequency C – V curve). Deep Level Transient Spectroscopy (DLTS) was used to analyze the interface traps and capture cross section present in the MFS capacitor. There were distinct peaks present in the DLTS spectrum and these peaks were attributed to the presence of the discrete interface states present at the semiconductor – ferroelectric interface. The distribution of calculated interface states were mapped with the silicon energy band gap for both the undoped and Ca doped BaTiO3 thin films using both the C – V and DLTS method. The interface states of the Ca doped BaTiO3 thin films were found to be higher than the pure BaTiO3 thin films.

Numerical simulations of CO2 migration during charnockite genesis

Charnockite is considered to be generated either through the dehydration of granitic magma by CO2 purging or by solid-state dehydration through CO2 metasomatism during granulite facies metamorphism. To understand the extent of dehydration, CO2 migration is quantitatively modeled in silicate melt and metasomatic fluid as a function of temperature, H2O wt%, pressure, basal CO2 flux and dynamic viscosity. Numerical simulations show that CO2 advection through porous and permeable high-grade metamorphic rocks can generate dehydrated patches close to the CO2 flow path, as illustrated by the occurrences of ``incipient charnockites.'' CO2 reaction-front velocity constrained by field observations is 0.69 km/m.y., a reasonable value, which matches well with other studies. On the other hand, temperature, rate of cooling, and basal CO2 flux are the critical parameters affecting CO2 diffusion through a silicate melt. CO2 diffusion through silicate melt can only occur at temperature greater than 840 degrees C and during slow cooling (<= 3.7 x 10(-5) degrees C/yr), features that are typical of magma emplacement in the lower crust. Stalling of CO2 fluxing at similar to 840 degrees C explains why some deep-level plutons contain both hydrous and anhydrous (charnockitic) mineral assemblages. CO2 diffusion through silicate melt is virtually insensitive to pressure. Addition of CO2 basal flux facilitates episodic dehydrated melt migration by generating fracture pathways.

Wide-Range Thermometry at Micro/Nano Length Scales with In2O3 Octahedrons as Optical Probes

We report the temperature-dependent photoluminescence and Raman spectra of In2O3 octahedrons synthesized by an evaporation condensation process. The luminescence obtained here is due to the defect-related deep level emission, which shows highly temperature-dependent behavior in 83-573 K range. Both the position as well as the intensity varies with temperature. Similarly, Raman spectroscopy in 83-303 K range shows temperature-dependent variation in peak intensity but no change in the peak position. Interestingly, the variation of intensity for different peaks is consistent with Placzek theory which invokes the possibility of temperature sensing. We demonstrate the reversibility of peak intensity with temperature for consecutive cycles and excellent stability of the octahedrons toward cryogenic temperature sensing. Overall, both the temperature-dependent photoluminescence and Raman spectra can be explored to determine temperature in the cryogenic range at micro/nano length scales. As an example, we evaluate the temperature-dependent Raman spectra of WO3 that undergoes a phase transition around 210 K and temperature-dependent luminescence of Rhodamine 6G (Rh6G) where intensity varies with temperature.

Nonvolatile holograms in LiNbO3 : Fe : Cu by use of the bleaching effect

We report our observation of a bleaching effect under an ultraviolet exposure in LiNbO3:Fe:Cu crystals. Two three-step recording-transferring-fixing schemes are proposed to record nonvolatile photorefractive holograms in such crystals. In the schemes two red laser beams and an ultraviolet illumination are used selectively to write the charge grating in the shallow-level Fe centers, to develop the charge grating in the deep-level Cu centers by transferring the charge grating in the Fe centers, and to fix only the charge grating in the Cu centers for unerasable read-out. Experimental results, verifications, and an optimal recording scheme are given. A comparison of the lithium niobate crystals of the same double-doping system of Fe:Mn, Ce:Mn, Ce:Cu, and Fe:Cu is outlined. (C) 2002 Optical Society of America.

Epitaxial growth of ZnO thin films on LiGaO2 substrates by pulsed-laser deposition

Lattice-matched (Delta(a/a) = 1.8-3.4%) (001) LiGaO2 substrates have been employed for the first time to grow ZnO thin films by pulsed-laser deposition at 350-650 degrees C with oxygen partial pressure of 20Pa. XRD shows that a highly c-axis-oriented ZnO film can be deposited on (001) LiGaO2 substrate at 500 degrees C. AFM images reveal the surfaces of as-deposited ZnO films are smooth and root-mean-square values are 6.662, 5.765 and 6.834 nm at 350, 500 and 650 degrees C, respectively. PL spectra indicate only near-band-edge UV emission appears in the curve of ZnO film deposited at 500 degrees C. The deep-level emission of ZnO film deposited at 650 degrees C probably results from Li diffusion into the film. All the results illustrate substrate temperature plays a pretty important role in obtaining ZnO film with a high quality on LiGaO2 substrate by pulsed-laser deposition. (c) 2006 Elsevier B.V. All rights reserved.

Annealing effect on properties of ZnO thin films grown on LiNbO3 substrates by MOCVD

ZnO films were grown on (0 0 0 1) LiNbO3 substrates by metal organic chemical vapor deposition (MOCVD). Annealing of ZnO films was performed in air for I h at 800 degrees C. The effects of annealing on the structural and optical properties of ZnO thin films on LiNbO3 substrates were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) measurements. XRD patterns and AFM showed that the as-grown and the annealed ZnO films grown on LiNbO3 substrates had c-axis preferential orientation, the crystallinity of the ZnO films grown on LiNbO3 Substrates was improved, and the grain size increased by annealing. The PL spectra showed that the intensity of the UV near-band-edge peak was increased after annealing, while the intensity of visible peak (deep-level emission) decreased. (c) 2005 Elsevier B.V. All rights reserved.

Growth and properties of ZnO thin film on beta-Ga2O3(100) substrate by pulsed laser deposition

Zinc oxide (ZnO) thin films were grown on the beta-Ga2O3 (100) substrate by pulsed laser deposition (PLD). X-ray diffraction (XRD) indicated that the ZnO films are c-axis oriented. The optical and electrical properties of the films were investigated. The room temperature Photoluminescence (PL) spectrum showed a near band emission at 3.28 eV with two deep level emissions. Optical absorption indicated a visible exciton absorption at room temperature. The as-grown films had good electrical properties with the resistivities as low as 0.02 Omega cm at room temperature. Thus, beta-Ga2O3 (100) substrate is shown to be a suitable substrate for fabricating ZnO film. (c) 2006 Elsevier B.V. All rights reserved.

Structure and UV emission of nanocrystal ZnO films by thermal oxidation of ZnS films

ZnO films prepared by the thermal oxidation of the ZnS films through thermal evaporation are reported. The as-deposited ZnS films have transformed to ZnO films completely at 400 degrees C. The 400-700 degrees C annealed films with a preferential c-axis (002) orientation have a hexagonal wurtzite structure. The band gap of ZnO films shifts towards longer wavelength with the increase of the annealing temperature. The relationship between the band gap energy of ZnO films and the grain size is discussed. The shift of the band gap energy can be ascribed to the quantum confinement effect in nanocrystal ZnO films. The photoluminescence spectra of ZnO films show a dominant ultraviolet emission and no deep level or trap state defect emission in the green region. It confirms the absence of interstitial zinc or oxygen vacancies in ZnO films. These results indicate that ZnO film prepared by this simple thermal oxidation method is a promising candidate for optoelectronic devices and UV laser. (c) 2005 Elsevier BN. All rights reserved.