J. G. Cederberg

INGAAS HETEROEPITAXY ON GAAS COMPLIANT SUBSTRATES : X-RAY DIFFRACTION EVIDENCE OF ENHANCED RELAXATION AND IMPROVED STRUCTURAL QUALITY

In0.44Ga0.56As (3% mismatch) films 3 μm thick were grown simultaneously on a conventional GaAs substrate, glass-bonded GaAs compliant substrates employing glasses of different viscosity, and a twist-bonded GaAs compliant substrate. High-resolution triple-crystal x-ray diffraction measurements of the breadth of the strain distribution in the films and atomic force microscopy measurements of the film’s surface morphology were performed. The films grown on the glass-bonded compliant substrates exhibited a strain distribution whose breadth was narrowed by almost a factor of 2 and a surface roughness that decreased by a factor of 4 compared to the film simultaneously grown on the conventional substrate. These improvements in the film’s structural quality were observed to be independent of the viscosity of the glass-bonding media over the range of viscosity investigated and were not observed to occur for the film grown on the twist-bonded substrate.

The effect of antimony in the growth of indium arsenide quantum dots in gallium arsenide (001)

The effect of an initial saturation coverage of antimony on the growth of indium arsenide quantum dots on gallium arsenide has been studied during metalorganic vapor-phase epitaxy. After depositing one to two bilayers of InAs at 723 K, the samples were quenched, transferred to ultrahigh vacuum, and characterized by scanning tunneling microscopy and x-ray photoelectron spectroscopy. It has been found that the critical thickness for onset of quantum dot formation is 33% less with Sb present as compared to without Sb. The antimony incorporates into the quantum dots, increasing their density and total volume, and causing them to be more densely clustered together.

Photoluminescence and free carrier interactions in erbium-doped GaAs

The photoluminescence properties of GaAs:Er doped with a new pyrazole and pyridine-based Er source, tris(3,5-di-tert-butylpyrazolato)bis(4-tert-butylpyridine)erbium(III), were investigated. These samples showed significantly stronger and sharper 1.54 μm Er3+ luminescence than in GaAs:Er samples doped with cyclopentadienyl-based Er sources. The efficient luminescence was associated with the Er–2O center, formed with unintentional oxygen impurities. The Er3+ emission was greatly reduced in n-type samples, whereas the emission remained strong in p-type samples. This trend suggests that either the free hole concentration is very important to the Er3+ excitation efficiency, and/or there is a strong Auger quenching mechanism which involves free electrons. A model based on the results of a two-beam experiment indicates the presence of strong Auger energy transfer from the Er-bound exciton to a free electron. Auger energy transfer from the excited Er3+ ion to a free electron was found to be much less important. T...

Incorporation of optically active erbium into GaAs using the novel precursor tris(3,5-di-tert-butylpyrazolato)bis(4-tert-butylpyridine)erbium

We have investigated the use of an alternative erbium precursor, tris(3,5-di-tert-butyl- pyrazolato)bis(4-tert-butylpyridine)erbium, to dope erbium into GaAs. The incorporated erbium forms an optically active center identified as Er–2O. The GaAs:Er formed using this precursor exhibits sharper and more intense optical emission, attributed to the Er–2O center, than that previously found with cylcopentadienyl-based erbium sources. Codoping GaAs:Er with shallow donors results in a quenching of the erbium-related luminescence, while codoping with shallow acceptors results in no significant change in the spectrum. Mechanisms for the observed luminescence-quenching behavior are discussed. Deep level transient spectroscopy performed on silicon or selenium codoped GaAs:Er showed the presence of several electron traps in the upper half of the band gap. The origins of these electron traps are considered.

Intrinsic and oxygen-related deep level defects in In0.5(AlxGa1−x)0.5P grown by metal-organic vapor phase epitaxy

Oxygen-related defects in An-containing semiconductors can degrade luminescence efficiency and reduce free carrier lifetime affecting the performance of light emitting devices. We have used the oxygen-doping source, diethylaluminum ethoxide, (C 2 H 5 ) 2 AlOC 2 H 5 , to intentionally incorporate oxygen-related defects during growth of In 0.5 (Al x Ga 1 -x ) 0.5 P by metal-organic vapor phase epitaxy (MOVPE). Our investigations have identified several defects which are present in nonintentionally oxygen-doped n-type In 0.5 (Al x Ga 1-x ) 0.5 P as well as those due to oxygen. Oxygen introduces defect states near the middle of the band gap. Deep level transient spectroscopy and photoluminescence data obtained over the range of composition 0 < x < 1, are presented illustrating the trends in defect structure with alloy composition.

Oxygen-related defects in low phosphorous content GaAs1−yPy grown by metal organic vapor phase epitaxy

The mixed Group V ternary alloy GaAs1−yPy (y<0.17) has been grown by metal organic vapor phase epitaxy and doped with oxygen using the oxygen precursor, diethylaluminum ethoxide [C2H5OAl(C2H5)2]. Controlled oxygen doping was accomplished over the range of 0<y<0.17. Deep level transient spectroscopy measurements reveal the presence of several oxygen-related deep levels. These levels, previously found in GaAs:O, vary with alloy composition over the investigated range. An additional deep level, most probably associated with the presence of misfit-related defects, has been identified. Photoluminescence performed on the oxygen-doped samples indicates that band edge emission is reduced and lower energy emission features are introduced over the wavelength range of 1000–1200 nm as a result of oxygen incorporation.

Photoluminescence studies on Al and Ga interdiffusion across (Al,Ga)Sb∕GaSb quantum well interfaces

The thermal interdiffusion of AlSb∕GaSb multiquantum wells was measured and the intrinsic diffusivities of Al and Ga determined over a temperature range of 823–948 K for 30–9000 s. The 77-K photoluminescence (PL) was used to monitor the extent of interdiffusion through the shifts in the superlattice luminescence peaks. The chemical diffusion coefficient was quantitatively determined by fitting the observed PL peak shifts to the solution of the Schrodinger equation, using a potential derived from the solution of the diffusion equation. The value of the interdiffusion coefficient ranged from 5.2×10−4 to 0.06nm2∕s over the conditions studied and was characterized by an activation energy of 3.0±0.1eV. The intrinsic diffusion coefficients for Al and Ga were also determined with higher values for Al than for Ga, described by activation energies of 2.8±0.4 and 1.1±0.1eV, respectively.

Influence of substrate doping and point defects on Al and Ga interdiffusion in AlSb/GaSb superlattice structures

Positron annihilation spectroscopy has been used to investigate the role of vacancies in the interdiffusion of Al and Ga in AlSb/GaSb superlattices. The samples were grown by metalorganic vapor-phase epitaxy on undoped and Te doped GaSb and consisted of ten periods of GaSb quantum wells (thickness 13 nm) and AlSb barriers (thickness 2–3 nm) and an approximately 50 nm thick capping layer of GaSb. The superlattices were annealed at 908 K for up to 250 s, resulting in interdiffusion of Al and Ga between well and barrier. A secondary ion mass spectrometry study showed that the Te dopant diffused from the substrate through the superlattice structure in the annealing process. In the positron annihilation study we observe that the vacancy concentration clearly decreases with annealing for the samples grown on undoped substrates, whereas the samples grown on Te doped substrates show a different annealing behavior.

Oxygen-Related Defects in In 0.5 (Al x Ga 1−x ) 0.5 P Grown by MOVPE

Oxygen related defects in Al-containing semiconductors have been determined to degrade luminescence efficiency and reduce free carrier lifetime, affecting the performance of light emitting diodes and laser diodes. We have used the oxygen doping source, diethylaluminum ethoxide, (C 2 H 5 ) 2 A1OC 2 H 5 , to intentionally incorporate oxygen-related defects during growth of In 0.5 (Al x Ga 1−x ) 0.5 P by Metalorganic Vapor Phase Epitaxy (MOVPE). Our investigations have identified several defects which are ‘intrinsic’ or present in non-intentionally oxygen-doped n-type In 0.5 (Al x Ga 1−x ) 0.5 P as well as those due to oxygen, which introduces defect states near the middle of the conduction band. Deep level transient spectroscopy and photoluminescence data obtained for these defects over a range of composition, are presented illustrating the trends in defect structure with alloy composition. The impact of oxygen contamination on the visible emission spectrum is presented and discussed in terms of the defect structure.

The surfactant effects of antimony on the formation of InAsSb nanostructures on GaAs by metal-organic chemical vapor deposition

We have investigated InAsSb nanostructures formed on GaAs during MOCVD. The transition thickness from 2D growth to 3D growth is reduced by the addition of TMSb/Sb 4 . This is consistent with both an increase in the adatom diffusion length and a reduction in the epilayer/vapor surface energy attributed TMSb/Sb 4 .