INVESTIGATION OF NEGATIVE TRANSIENT CURRENT OF ARGON-IMPLANTED GAAS USING PHOTOINDUCED TRANSIENT-CURRENT SPECTROSCOPY

The investigation of deep levels of argon-implanted LEC-grown semi-insulating GaAs with implantation dosages ranging from 1 x 10(11) to 1 x 10(15) cm-2 has been performed. Using a photoinduced transient-current spectroscopy (PITCS) it was demonstrated that, for implantation dosages below 1 X 10(13) cm-2, a negative peak or negative transient current (NTC) was observed in the temperature range from 330 to 350 K. The magnitude of this negative peak increased with dosage up to a level of 1 X 10(12) cm-2, beyond which it decreased with dosage. The dosage dependence of the EL3 peak height and the resistance of the specimen have also been investigated. It was observed that the variation of the EL3 peak height with dosage was similar to the variation of the magnitude of the negative peak, that is the EL3 peak height likewise increased with dosage up to 1 X 10(12) cm-2, and then decreased. The resistance of the original high-resistivity specimen dropped abruptly when the dosage reached 1 X 10(12) cm-2. This critical dosage (1 X 10(12) cm-2) was found to be a threshold for the generation of a highly disordered state.

Stoichiometric defects in semi-insulating GaAs

The influences of arsenic interstitials and dislocations on the lattice parameters of undoped semi-insulating (SI) GaAs single crystals were analyzed. It was shown that the dislocations in such crystals serve as effective gettering sites for arsenic interstitials due to the deformation energy of dislocations. The average excess arsenic in GaAs epilayers grown by molecular-beam epitaxy (MBE) at low temperatures (LT) is about 1%, and the lattice parameters of these epilayers are larger than those of liquid-encapsulated Czochralski-grown (LEG) SI-GaAs by about 0.1%. The atomic ratio, [As]/([Ga] + [As]), in SI-GaAs grown by low-pressure (LP) LEC is the nearest to the strict stoichiometry compared with those grown by high-pressure (HP) LEC and vertical gradient freeze (VGF). After multiple wafer annealing (MWA), the crystals grown by HPLEC become closer to be strictly stoichiometric.

VGF法生长的低位错掺Si-GaAs单晶的缺陷和性质

研究了垂直梯度凝固法（VGF法）生长的掺Si低阻GaAs单晶材料的晶格缺陷和性质,并将VGF法和LEC法生长的非掺半绝缘GaAs单晶进行了比较.利用A-B腐蚀显微方法比较了两种材料中的微沉积缺陷,对其形成原因进行了分析.利用荧光光谱研究了掺Si-GaAs单晶中Si原子和B原子的占位情况和复合体缺陷.Hall测量结果表明,掺Si低阻VGF-GaAs单晶中存在很强的Si自补偿效应,造成掺杂效率降低.VGF-GaAs单晶生长过程中高的Si掺杂浓度造成晶体中产生大量杂质沉积,而杂质B的存在加重了这种现象.对降低缺陷密度,提高掺杂效率的途径进行了分析.

高温退火处理提高半绝缘VGF-GaAs单晶的电学性能

垂直梯度凝固法（VGF）生长的低位错半绝缘（SI）GaAs单晶存在电阻率和迁移率低、电学补偿度小、均匀性差等问题.在3种不同温度条件下,对VGF-SI-GaAs晶片进行了加As压的闭管退火处理.结果表明,经过1160℃/12h的高温退火处理后,VGF-SI-GaAs单晶的电阻率、迁移率和均匀性均得到了显著提高.利用Hall、热激电流谱（TSC）、红外吸收法分别测试分析了原生和退火VGF-SI-GaAs单晶样品的电学性质、深能级缺陷、EL2浓度和C浓度,并与常规液封直拉法（LEC）SI-GaAs单晶样品进行了比较.原生VGF-SI-GaAs单晶中的EL2浓度明显低于LEC-SI-GaAs单晶,经过退火处理后其EL2浓度显著增加,电学补偿增强,而且能级较浅的一些缺陷的浓度降低,因而有效提高了其电学性能.

高质量InAs单晶材料的制备及其性质

利用液封直拉法（LEC）生长了直径50mm〈100〉和（111〉晶向的InAs单晶．分析研究了n型杂质Sn，S和p型杂质Zn，Mn的分凝特性、晶格硬化作用、掺杂效率等．利用X射线双晶衍射分析了晶体的完整性．对InAs晶片的抛光、化学腐蚀和清洗进行了分析，在此基础上实现了抛光晶片的开盒即用（EPI—READY）．

Preparation of Semi-Insulating Material by Annealing Undoped InP

Semi-insulating (SI) InP wafers of 50 and 75mm in diameter can be obtained by annealing of undoped liquid encapsulated Czochralski (LEC) InP at 930 ℃ for 80h. The annealing ambient can be pure phosphorus (PP) or iron phosphide (IP). The IP-SI InP wafers have good electrical parameters and uniformity of whole wafer. However, PP-SI InP wafers exhibit poor uniformity and electrical parameters, Photoluminescence which is subtle to deep defect appears in IP-annealed semi-insulating InP. Traps in annealed SI InP are detected by the spectroscopy of photo-induced current transient. The results indicate that there are fewer traps in IP-annealed undoped SI InP than those in as-grown Fe-doped and PP-undoped SI-undoped SI InP. The formation mechanism of deep defects in annealed undoped InP is discussed.

半绝缘GaAs衬底中位错对MESFETs旁栅效应的影响

在位错密度不同的LEC半绝缘(SI)GaAs衬底上离子注入制做MESFETs,观察衬底位错对MESFETs旁栅效应的影响。结果表明，衬底中高位错密度可以拟制旁栅效应。

Twin and grain boundary in InP: A synchrotron radiation study

Experimentally observed X-ray reflectivity curves show bi-crystal(twin) characteristics. The study revealed that there was defect segregation at the twin boundary. Stress was relaxed at the edge of the boundary. Relaxation of the stress resulted in formation of twin and other defects. As a result of formation of such defects, a defect-free and stress-free zone or low defect density and small stress zone is created around the defects. So a twin model was proposed to explain the experimental results. Stress(mainly thermal stress), chemical stoichiometry deviation and impurities nonhomogeneous distributions are the key factors that cause twins in LEC InP crystal growth. Twins on (111) face in LEC InP crystal were studied. Experimental evidence of above mentioned twin model and suggestions on how to get twin-free LEC InP single crystals will be discussed.

Characterization of defects and whole wafer uniformity of annealed undoped semi-insulating InP wafers

Semi-insulating (SI) InP wafers of 2 and 3 in. diameters have been prepared by annealing undoped LEC InP at 930 degreesC for 80 h under pure phosphorus ambient (PP) and iron phosphide ambient (IP). The electrical uniformity of annealed undoped SI wafers, along with a Fe-doped as-grown SI LEC InP wafer, has been characterized by whole wafer PL mapping and radial Hall measurements. Defects in these wafers have been detected by photo-induced current transient spectroscopy (PICTS). The results indicated that the uniformity of IP wafer is much better than that of PP wafer and as-grown Fe-doped Si InP wafer. There are fewer traps in undoped SI InP IP wafer than in as grown Fe-doped and undoped SI InP PP wafer, as evidenced by PICTS. The good uniformity of the IP wafer is related to the nonexistence of high concentration of thermally induced defects. The mechanism for this phenomenon is discussed based on the results. (C) 2002 Elsevier Science B.V. All rights reserved.

Semi-insulating GaAs grown in outer space

A semi-insulating GaAs single crystal ingot was grown in a recoverable satellite, within a specially designed pyrolytic boron nitride crucible, in a power-traveling furnace under microgravity. The characteristics of a compound semiconductor single crystal depends fundamentally on its stoichiometry, i.e. the ration of two types of atoms in the crystal. a practical technique for nondestructive and quantitative measuring stoichiometry in GaAs single crystal was used to analyze the space-grown GaAs single crystal. The distribution of stoichiometry in a GaAs wafer was measured for the first time. The electrical, optical and structural properties of the space-grown GaAs crystal were studied systematically, Device fabricating experiments prove that the quality of field effect transistors fabricated from direct ion-implantation in semi-insulating GaAs wafers has a close correlation with the crystal's stoichiometry. (C) 2000 Elsevier Science S.A. All rights reserved.

P-选择素CR结构域功能的模拟预测

<正>选择素(selectin)与其配体间相互作用介导的细胞粘附在炎症级联反应、肿瘤转移和淋巴细胞归巢等病理、生理过程中起重要作用。其结构组成从远离细胞表面的N-末端到胞内C-末端,依次为:钙型凝集素功能区(Calcium-type lectin domain,Lec),类上皮生长因子功能区(Epidermal Growth Factor-like module,EGF),具有粘附补体蛋白作用的多个重复序列(Consensus Repeats,CRs),跨膜区(Transmembrane,TM)和胞内区

P-选择素Lectin结构域变构的模拟预测

<正>粘附分子选择素(selectin)家族成员与其配体间相互作用介导的细胞粘附在炎症级联反应、肿瘤转移和淋巴细胞归巢等病理、生理过程中起重要作用(Bevilacqua and Nelson,1993)。其结构组成从远离细胞表面的N-末端到胞内C-末端,依次为:钙型凝集素功能区(Calcium-type lectin domain,Lec),类上皮生长因子功

Identification of a C-type lectin from the bay scallop Argopecten irradians

C-type lectins are Ca2+ dependent carbohydrate-recognition proteins that play crucial roles in the invertebrate innate immunity, such as nonself recognition, activation of proPO system, antibacterial activity, promotion of phagocytosis and nodule formation. In this study, a novel C-type lectin of bay scallops Argopecten irradians (Ai Lec) was identified using expressed sequence tag (EST) and RACE techniques. The Ai Lec cDNA encoded a polypeptide of 171 amino acids with a putative signal peptide of 21 amino acid residues and a mature protein of 150 amino acids. The deduced amino acid sequence of Ai Lec was highly similar to those of the C-type lectins from other animals and contained a typical carbohydrate-recognition domain (CRD) of 131 residues, which has four conserved disulfide-bonded cysteine residues that define the CRD and two additional cysteine residues at the amino terminus. The expression of Ai Lec transcript was dominantly detected in the hepatopancreas and slightly detected in the haemocytes of normal scallops. 6 h after Vibrio anguillarum-challenge and 8 h after Micrococcus luteus-challenge, the temporal expression of Ai Lec mRNA in hemocytes was increased by 4.4- and 3.6-folds, respectively. The results suggested that Ai Lec was a constitutive and inducible acute-phase protein and might be involved in immune response to Gram-negative and Gram-positive microbial infection in bay scallop A. irradians.

Estudios sobre el género Tulostoma y Geastrum (Gasteromycetes)

Se realiza un estudio macro y microscópico de Geastrum campestre (Morgan) Kamblev & Lec y G. saccatum (Fr.) Fischer. Se amplia la corolooia de Tulostoma giovanellae Bresad. hasta ahora conocido en España peninsular de la region Mediterránea al centro peninsular. Se propone la sinonimia de Tulostoma campestre Morgan a T. fimbriatum Fr.

Effect of short-term macrophage depletion in the development of posterior capsule opacification in rodents

Aim: To evaluate the role of macrophages in the development of posterior capsule opacification (PCO). Methods: For this purpose, an extracapsular lens extraction was performed in 18 consecutive Sprague-Dawley rats. Animals were treated with liposomal clodronate (Cl MDP-lip-treated group, n = 10) or phosphate-buffered saline (PBS) (control group, n = 8) 1 day preoperatively and on the first day postoperatively, and sacrificed 3 days postoperatively. Masked clinical, light microscopy and immunohistochemistry studies were conducted. The Fisher exact test and randomisation test were used to assess statistically differences between groups. Results: A statistically significant reduction in the number of macrophages (ED1+, ED7+, ED8+) was found in the Cl MDP-lip-treated group compared with the PBS-lip-treated group (p = 0.048, p = 0.004, p = 0.027, respectively). There were no statistically significant differences with regards to the presence/absence of central opacification (p = 0.29) and capsular wrinkling (p = 0.21) as detected clinically between groups. Similarly, a qualitative evaluation of the degree of PCO with regards to lens epithelial cell (LEC) proliferation, capsular wrinkling and Soemmerring ring formation showed no statistically significance between groups (p = 0.27, p = 0.061, p = 1.0, respectively). However, a statistically significant reduction in the number of lens epithelial cells (LEC) counted in the centre of the posterior capsule was found in the Cl MDP-lip- treated group (p = 0.009). Conclusion: Depletion of macrophages was accompanied by a reduction in LEC in the centre of the posterior capsule in rodents.