摘要:

A room-temperature photoelectrochemical etching process forn-type GaN films using a 0.04 M KOH solution and Hg arc lamp illumination is described. The process provides highly anisotropic etch profiles and high etch rates (>300 nm/min) at moderate light intensities (50mW/cm2&at;365 nm). The etch rate and photocurrent are characterized as a function of light intensity for stirred and unstirred solutions, and the etch process is found to be diffusion limited for light intensities greater than 20mW/cm2&at;365 nm. A reaction mechanism for the etch process is proposed. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119365

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated the spectral response of front-surface-illuminated GaN and AlGaN/GaNp-i-nultraviolet photodetectors prepared by reactive molecular beam epitaxy on sapphire substrates. GaN homojunctionp-i-nphotodiodes exhibited a peaked response near the band edge. This enhanced response was absent in the AlGaN/GaN heterojunctionp-i-ndetectors. We analyzed the effect ofp-layer thickness of the GaNp-i-ndiodes on the magnitude of the peak photoresponse. The AlGaN/GaN photodiodes had a maximum zero-bias responsivity of 0.12 A/W at 364 nm, which decreased by more than 3 orders of magnitude for wavelengths longer than 390 nm. A reverse bias of −10 V raised the responsivity to 0.15 A/W without any significant increase in noise. The root-mean-square noise current in a 1 Hz bandwidth is ∼1.0 pA, corresponding to a noise-equivalent-power of ∼8.3 pW. We measured extremely fast decay times of 12 ns for the AlGaN/GaN and 29 ns for the GaN photodiodes. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119366

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Raman analysis of theE2mode ofAlxGa1−xNin the composition range0⩽x⩽1is presented. The line shape was observed to exhibit a significant asymmetry and broadening toward the high energy range. The spatial correlation model is discussed, and is shown to account for the line shape. The model calculations also indicate the lack of a long-range order in the chemical vapor deposition alloys. These results were confirmed by x-ray scattering: the relative intensity of the superlattice line was found to be negligible. The line broadening of theE2mode was found to exhibit a maximum at a compositionx≅0.5indicative of a random disordered alloy system. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119367

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the electron and hole drift mobilities and the recombination lifetime in thin polycrystallineC60films. The data are obtained from photocurrent measurements involving an optical interference grating moving at variable velocity across the sample surface. Considerable degradation of the transport parameters is observed as the samples are exposed to air. The initial values for the electron and hole drift mobilities are1.3±0.2 cm2/V sand(2±1)×10−4 cm2/V s,respectively, and for the recombination lifetime(1.7±0.2)×10−6s. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119368

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We grew coherent Ge islands on Si(113) substrates by molecular beam epitaxy. Atomic force microscopy and reflection high energy electron diffraction were used to examine surface morphology as a function of Ge coverage and growth temperature. The as-grown coherent islands were shaped like wires and formed dense arrays over the entire surface. The islands bounded by {519} facets were elongated in the [332¯] direction and were linearly ordered across steps. The wire-shaped islands formed when Ge coverage was 5–8 monolayers and the growth temperature was 400–500 °C. Cross-sectional transmission electron microscope images confirm that the Ge islands are coherently grown on the Si substrates. The anisotropic shape of the Ge islands was due to an anisotropic strain relief mechanism on Si(113), which had been theoretically predicted. Our findings suggest that the coherent island formation of Ge on Si(113) may be a possible method to fabricate self-assembled Ge nanowires. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.119369

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Photoluminescence (PL) and Raman spectra were measured along a cross section of porous silicon films at different oxidation times after application of anodic current transients. The average crystallite size was determined from the Raman spectra with the standard phonon confinement model. Before oxidation, the PL emission energy and crystallite size were found to be independent of the layer depth. Also, the integrated PL emission was larger for the middle layers. The effect of oxidation was a blueshift of the PL band and a decrease in the integrated emission for the outer layers. The crystallite size increases for all layers, particularly the outer ones. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119370

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Atomic hydrogen, produced at a hot wire, passivates bulk defects in polycrystalline silicon without damaging surface regions. Solar cells from such polycrystalline silicon respond much more favorably to hot-wire hydrogenation than to low-energy ion implantation or a direct-current plasma treatment. Hot-wire passivation yields a hydrogen concentration close to the surface of 8×1019cm−3and improves the minority carrier diffusion length of solar cells by up to 100&percent;. Implantation as well as conventional plasma treatment result in lower hydrogen concentration and, consequently, in much smaller improvements of diffusion lengths. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119371

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Near band edge photoluminescence (PL) is observed from about 100-nm-thick pseudomorphicSi1−yCyepilayers, which were grown by molecular beam epitaxy on a Si substrate. Different pieces of one wafer were annealed at temperatures between 500 and 800 °C, and it is shown that annealing leads to increased PL intensities and reduced linewidths. The smallest achieved full width at half maximum was 8.6 meV. We also observe a blueshift of the PL lines after annealing, which does not correspond to the minor changes in the amount of substitutional carbon deduced from x-ray measurements. Temperature dependent PL measurements suggest that the recombination involves electrons localized at alloy fluctuations. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119372

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thermal decomposition of an amido precursor; [Ga2(NMe2)6,Me=CH3] in an ammonia atmosphere yielded nanostructured gallium nitride powder. The x-ray diffraction spectrum of the nanosized gallium nitride exhibited reflections corresponding to the lattice planes of fcc (zinc blende) GaN. High resolution transmission electron microscopy confirmed the cubic structure of the material and evidence of stacking faults within the fcc structure. Infrared spectra showed the characteristic Ga–N stretch at550 cm−1.Transmission electron microscope measurements indicated that the GaN consisted of≈50 nmsized particles which in turn are agglomerates of smaller particles with ≈5 nm domain sizes. The photoluminescence (PL) emission spectrum of the GaN was found to be sensitive to the excitation wavelength exhibiting peaks at 378 and 317 nm. The PL excitation spectrum showed resonances in the 200–300 nm region. These PL results suggest the effect of quantum confinement in these GaN particles. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119565

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a scanning tunneling microscopy (STM) study of the initial stages of ZnSe deposition on the GaAs(001)-(2×4)surface. The deposition of elemental Se and of ZnSe on the bare GaAs surface induces considerable atomic disorder attributed to the Se–As exchange reaction. The deposition of elemental Zn weakens the2×periodicity of the surface but induces no apparent changes in the STM images of the As dimers. Comparison of STM images of submonolayers of ZnSe on GaAs with and without a Zn pretreatment suggests that Zn reduces the interaction of Se with the GaAs surface. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119373

出版商:AIP    

年代:1997

数据来源: AIP