The effect of Be-doping structure in negative electron affinity GaAs photocathodes on integrated photosensitivity

A new structure of GaAs photocathode was introduced. The Be-doping concentration is variable in the new structure compared with the constant concentration of Be in the normal photocathode. Negative electron affinity GaAs photocathodes were fabricated by alternate input of Cs and O. The spectral response results measured by the on-line spectral response measurement system show that the integrated photosensitivity of the photocathodes with the new structure is enhanced by at least 50% as compared to those with the monolayer structure. Accordingly, two main factors leading to the enhanced photosensitivity of the photocathodes were discussed. (c) 2005 Elsevier B.V. All rights reserved.

Aluminium doping induced enhancement of p-d coupling in ZnO

Valence-band type Auger lines in Al doped and undoped ZnO were comparatively studied with the corresponding core level x-ray photoelectron spectrography (XPS) spectra as references. Then the shift trend of energy levels in the valence band was that p and p-s-d states move upwards but e and p-d states downwards with increasing Al concentration. The decreased energy of the Zn 3d state is larger than the increased energy of the 0 2p state, indicating the lowering of total energy. This may indicate that Al doping could induce the enhancement of p-d coupling in ZnO, which originates from stronger Al-O hybridization. The shifts of these states and the mechanism were confirmed by valence band XPS spectra and 0 K-edge x-ray absorption spectrography (XAS) spectra. Finally, some previously reported phenomena are explained based on the Al doping induced enhancement of p-d coupling.

Magnetism and luminescence evolution due to nitrogen doping in manganese-gallium oxide nanowires

We report a new method for large-scale production of GaMnN nanowires, by annealing manganese-gallium oxide nanowires in flowing ammonia at high temperature. Microstructure analysis indicates that the GaMnN nanowires have wurtzite GaN structure without Mn precipitates or Mn-related second phases. Magnetism evolution due to nitrogen doping in manganese-gallium oxide nanowires was evaluated by magnetic measurements. Magnetic measurement reveals that the magnetization increases with the increase of nitrogen concentration. Ferromagnetic ordering exists in the GaMnN nanowires, whose Curie temperature is above room temperature. Luminescence evolution was investigated by the cathodoluminesence measurement for a single nanowire and photoluminescence measurement in a temperature range between 10 and 300 K. Experimental results indicate that optical properties can be modulated by nitrogen doping in manganese-gallium oxide nanowires. (c) 2005 Elsevier B.V. All rights reserved.

Silicon doping induced increment of quantum dot density

Low-indium-content self-assembled InGaAs/GaAs quantum dots (SAQD) were grown using solid-source molecular beam epitaxy (MBE) and investigated by atomic force microscopy and photoluminescence (PL) spectroscopy. Silicon, which was doped at different quantum dot (QD) growth stages, markedly increased the density of QD. We obtained high density In0.35Ga0.65As/GaAs(001) quantum dots of 10(11)/cm(2) at a growth temperature of 520degreesC. PL spectra and distribution statistics show the high quality and uniformity of our silicon-doped samples. The density increment can be explained using the lattice-hardening mechanism due to silicon doping.

In situ doping of 3C-SiC grown on (0001) sapphire substrates by LPCVD

The heteroepitaxial growth of n-type and p-type 3C-SiC on (0001) sapphire substrates has been performed with a supply of SiH4+C2H4+H-2 system by introducing ammonia (NH3) and diborane (B2H6) precursors, respectively, into gas mixtures. Intentionally incorporated nitrogen impurity levels were affected by changing the Si/C ratio within the growth reactor. As an acceptor, boron can be added uniformly into the growing 3C-SiC epilayers. Nitrogen-doped 3C-SiC epilayers were n-type conduction, and boron-doped epilayers were p-type and probably heavily compensated.

Effect on the optical properties and surface morphology of cubic GaN grown by metalorganic chemical vapor deposition using isoelectronic indium surfactant doping

The surfactant effect of isoelectronic indium doping during metalorganic chemical vapor deposition growth of cubic GaN on GaAs (1 0 0) substrates was studied. Its influence on the optical properties and surface morphology was investigated by using room-temperature photoluminescence (PL) and atomic force microscopy. It is shown that the sample with small amount of In-doping has a narrower PL linewidth, and a smoother surface than undoped cubic GaN layers. A slight red shift of the near-band-edge emission peak was observed. These results revealed that, for small TMIn flow rates, indium played the role of the surfactant doping and effectively improved the cubic GaN film quality; for large TMIn flow rates, the alloying formation of Ga1-xInxN might have occurred. (C) 2002 Elsevier Science B.V. All rights reserved.

Indium doping effect on GaN in the initial growth stage

Three minutes' growth was carried out to investigate the indium-doping effect on initially grown GaN. Indium-doped and undoped samples were grown by low-pressure metalorganic vapor phase epitaxy. Atomic force microscope observation revealed that In-doping modified the morphology of the nuclei. Indium-doping also enhanced wetting between the buffer and nuclei layers, which was also supported by optical transmission. Photoluminescence suggested that indium-doping obviously enhanced band-edge related emission even in the nucleation stage. X-ray diffraction performed on samples grown for 20 minutes indicated improvement of the crystalline quality through indium-doping. The mechanism of the indium-doping effect was discussed.

In situ annealing treatment and In-doping of GaN epilayers grown by MOVPE

The effects of in situ annealing treatment in the initial growth stage and In-doping during growth of the GaN on the material properties were investigated. GaN was grown by LP-MOVPE. In situ annealing reduced the full-width at half-maximum (FWHM) of X-ray rocking curves and reduced etch pit density of GaN films. It improved the optical properties of the epilayer. Undoped and In-doped GaN films of initial growth stage were investigated. It was found that morphology and optical properties were improved in In-doped samples. (C) 2000 Elsevier Science B.V. All rights reserved.

Doping during low-temperature growth of materials for n-p-n Si/SiGe/Si heterojuction bipolar transistor by gas source molecular beam epitaxy

In situ doping for growth of n-p-n Si/SiGe/Si heterojuction bipolar transistor (HBT) structural materials in Si gas source molecular beam epitaxy is investigated. We studied high n-type doping kinetics in Si growth using disilane and phosphine, and p-type doping in SiGe growth using disilane, soild-Ge, and diborane with an emphasis on the effect of Ge on B incorporation. Based on these results, in situ growth of n-p-n Si/SiGe/Si HBT device structure is demonstrated with designed structural and carrier profiles, as verified from characterizations by X-ray diffraction, and spreading resistance profiling analysis. (C) 2000 Elsevier Science B.V. All rights reserved.

Effect of Si doping on cubic GaN films grown on GaAs(100)

Epitaxial layers of cubic GaN have been grown by metalorganic vapor-phase epitaxy (MOVPE) with Si-doping carrier concentration ranging from 3 x 10(18) to 2.4 x 10(20)/cm(3). Si-doping decreased the yellow emission of GaN. However, the heavily doped n-type material has been found to induce phase transformation. As the Si-doping concentration increases, the hexagonal GaN nanoparticles increase. Judged from the linewidth of X-ray rocking curve, Si-doping increases the density of dislocations and stacking faults. Based on these observations, a model is proposed to interpret the phase transformation induced by the generated microdefects, such as dislocations and precipitates, and induced stacking faults under heavy Si-doping. (C) 1999 Elsevier Science B.V. All rights reserved.

Si doping effect on self-organized InAs/GaAs quantum dots

In situ ultra high vacuum scanning probe microscopy (SPM) and low-temperature :photoluminescence (PL) studies have been performed on Si-doped self-organized InAs/GaAs quantum dots samples to investigate the Si doping effects. Remarkably, when Si is doped in the sample, according to the SPM images, more small dots are formed when compared with images from undoped samples. On the PL spectra, high-energy band tail which correspond to the small dots appear, with increasing doping concentration, the integral intensity of the high-energy band tail account for the whole peak increase too. We relate this phenomenon to a model that takes the Si atom as the nucleation center for QDs formation. (C) 1999 Elsevier Science B.V. All rights reserved.

High phosphorous doping and morphological evolution during Si growth by gas source molecular beam epitaxy (GSMBE)

Uniform and high phosphorous doping has been demonstrated during Si growth by GSMBE using disilane and phosphine. The p-n diodes, which consist of a n-Si layer and a p-SiGe layer grown on Si substrate, show a normal I-V characteristic. A roughening transition during P-doped Si growth is found. Ex situ SEM results show that thinner film is specular. When the film becomes thicker, there are small pits of different sizes randomly distributed on the flat surface. The average pit size increases, the pit density decreases, and the size distribution is narrower for even thicker film. No extended defects are found at the substrate interface or in the epilayer. Possible causes for the morphological evolution are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.

p-type co-doping study of GaN by photoluminescence

Photoluminescence measurements were performed on p-type co-doping effects of C, As, and Mg in GaN. The dopants were incorporated into GaN by ion implantation performed at 77 K. We find that the 3.42 eV luminescence line is sensitive to hole concentration, and propose that after cartful calibration the 3.42 eV line may be used as a probe to measure hole concentration in GaN. Simply doping one kind of accepters will not result in holes, while co-doping can substantially improve p-type doping efficiency. As + C and As + Mg co-doping induce an acceptor level of 180 meV above the valence band. Mg + C co-doping is the most promising method for p-type doping, the related acceptor level is determined to be as shallow as 130 meV. The improvement of the doping efficiency by co-doping is probably due to the decrease of the acceptor ionization energy. (C) 1999 Elsevier Science B.V. All rights reserved.

In-Situ Boron and Aluminum Doping and Their Memory Effects in 4H-SiC Homoepitaxial Layers Grown by Hot-Wall LPCVD

The in-situ p-type doping of 4H-SiC grown on off-oriented (0001) 4H-SiC substrates was performed with trimethylaluminum (TMA) and/or diborane (B2H6) as the dopants. The incorporations of Al and B atoms and their memory effects and the electrical properties of p-type 4H-SiC epilayers were characterized by secondary ion mass spectroscopy (SIMS) and Hall effect measurements, respectively. Both Al- and B-doped 4H-SiC epilayers were p-type conduction. It was shown that the profiles of the incorporated boron and aluminum concentration were in agreement with the designed TMA and B2H6 flow rate diagrams. The maximum hole concentration for the Al doped 4H-SiC was 3.52x10(20) cm(-3) with Hall mobility of about 1 cm(2)/Vs and resistivity of 1.6 similar to 2.2x10(-2) Omega cm. The heavily boron-doped 4H-SiC samples were also obtained with B2H6 gas flow rate of 5 sccm, yielding values of 0.328 Omega cm for resistivity, 5.3x10(18) cm(-3) for hole carrier concentration, and 7 cm(2)/VS for hole mobility. The doping efficiency of Al in SiC is larger than that of B. The memory effects of Al and B were investigated in undoped 4H-SiC by using SIMS measurement after a few run of doped 4H-SiC growth. It was clearly shown that the memory effect of Al is stronger than that of B. It is suggested that p-type 4H-SiC growth should be carried out in a separate reactor, especially for Al doping, in order to avoid the join contamination on the subsequent n-type growth. 4H-SiC PiN diodes were fabricated by using heavily B doped epilayers. Preliminary results of PiN diodes with blocking voltage of 300 V and forward voltage drop of 3.0 V were obtained.

The difference of Si doping efficiency in GaN and AlGaN in GaN-based HBT structure

An AlGaN/GaN HBT structure was grown by low-pressure metalorganic chemical vapor deposition (MOCVD) on sapphire substrate. From the high-resolution x-ray diffraction and transmission electron microscopy (TEM) measurements, it was indicated that the structure is of good quality and the AlGaN/GaN interfaces are abrupt and smooth. In order to obtain the values of Si doping and electronic concentrations in the AlGaN emitter and GaN emitter cap layers, Secondary Ion Mass Spectroscopy (SIMS) and electrochemical CV measurements were carried out. The results showed that though the flow rate of silane (SiH4) in growing the AlGaN emitter was about a quarter of that in growing GaN emitter cap and subcollector layer, the Si sputtering yield in GaN cap layer was much smaller than that in the AlGaN emitter layer. The electronic concentration in GaN was about half of that in the AlGaN emitter layer. It is proposed that the Si, Al co-doping in growing the AlGaN emitter layer greatly enhances the Si dopant efficiency in the AlGaN alloy. (c) 2006 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim.