L. Jedral

Photo-assisted chemical transport reaction growth of ZnS on GaP

Abstracts are not published in this journal

Optical characterization of AlInGaAs/InGaAs quantum well structures on InGaAs substrates

We report on photoluminescence and photoreflectance studies of metalorganic chemical vapor deposition grown InGaAs/InGaAlAs quantum well structures on lattice matched InGaAs substrates. The optical characteristics of the substrates are also discussed. The quantum wells exhibit a high degree of relaxation, despite their thickness being below the critical values, which may be related to the growth conditions. A correlation was found between the optical characteristics and the quality of the layer structures grown on the InGaAs substrates.

Semiconductor based light emitters powered by tritium

We report on radioluminescence (RL) studies of the wide band gap semiconductors GaP and GaInAsP exposed to tritium gas. All samples were prepared by liquid phase epitaxy. RL tests were performed as a function of tritium pressure, sample temperature, and time, enabling the limiting factors for developing high efficiency visible RL sources to be identified. The studies were complemented by photoluminescence (PL) and cathodoluminescence (CL) measurements. Reduction of surface recombination velocity was shown to be essential for obtaining low threshold CL response and improved PL efficiency. This factor resulted in tritium-activated RL visible to the naked eye. With appropriate materials optimization, these structures should be suitable for developing high efficiency RL devices.

Passivation Studies on AlGaAs Surfaces Suitable for High Power Laser Development

We report on the optical characterization of sulphur (S) passivated Al x Ga 1−x As/GaAs surfaces using photoluminescence (PL) and surface photovoltage (SPV) measurements. Both techniques show an enhancement in the near bandgap signal intensity, implying a reduction of the non-radiative recombination rate at the surface. To counter the instability of S-passivation, due to re-oxidation, dielectric layers of silicon nitride were deposited using electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD); the deposition of dielectric layers up to lOOnm thick does not appear to cause significant deterioration or stress at the insulator/AlGaAs interface. The dielectric layers are shown to be resistant to oxidation, and effective in maintaining the passivation effect over a period of weeks.

Optical characterization of passivation for high-power AlxGa1-xAs-based lasers

We report on passivation of AlxGa1-xAs/GaAs surfaces using different sulfur and chlorine based treatments: These include ammonium sulfide solution, arsenic sulfide vapor and hydrochloric acid treatments. Enhancements in the intensity of near band-gap photoluminescence (PL) peaks, coupled with peak half-width reduction on treatment were attributed to a reduction in the density of surface states. Pre-etching using sulfuric acid- and ammonium hydroxide-based solutions prior to sulfur passivation was also found to contribute significantly to the overall success of a passivation treatment. The best sulfur-passivation results for all x (0 < x < 0.38) were found when sulfuric acid-peroxide-deionized water (Caros) solution pre-etching was followed by ammonium sulfide solution treatment at 65 degree(s)C for 25 min.

Electronic properties of InGaAsP epitaxial layer surfaces

Abstract We report on studies of the surface properties of InGaAsP epitaxial layers. A strong correlation was found between the near-surface band structure and the luminescent efficiencies. Sulfur treatment strongly influenced carrier recombination dynamics by altering the near-surface field. This profoundly effected electrical and optical properties of the layers.

Optical characterization of low-temperature GaAs

Molecular beam expitaxial (MBE) grown GaAs at low substrate temperature (LT-GaAs) possesses a unique combination of properties (i.e., semi-insulation and short carrier lifetime) that has led to a variety of electronic and photonic device applications. In this paper, we report on the optical characterization of LT-GaAs, including carrier lifetime, photoreflectance (PR), and surface photovoltage (SPV) measurements. The undoped LT-GaAs samples were grown using our ow custom designed MBE system at the following substrate temperatures: 200 degree(s)C, 250 degree(s)C and 300 degree(s)C. These sample were then annealed at 7000-850 degree(s)C in a rapid thermal annealing (RTA) system. The PR spectra revealed that the PR amplitude depends strongly on the carrier lifetime, while the PR spectral broadening of near bandgap peak depends strongly on the internal field non-uniformly caused by buried Schottky barriers around the As precipitates. Above bandgap SPV measurements revealed a unique SPV spectrum compared with that for bulk GaAs. Carrier lifetime was measured for LT-GaAs samples grown at 200, 250, and 300 degree(s)C, respectively, and annealed at 700 degree(s)C for 30 seconds, and the corresponding carrier lifetimes at 1.5, 2.2, and 12 ps.

Orientation Dependence Of Surface Passivation For Semi-Insulating Gaas

We report on the orientation dependence ((100), (110) and (111) ) of photoluminescence (PL), photoreflectance (PR) and Surface Photo-Voltage (SPV) for sulfur passivated bulk semiinsulating (SI) GaAs. Near band gap PL peak intensities (bound-exciton and acceptor-related) were enhanced following (NH 4 ) 2 S or S 2 Cl 2 treatment of GaAs for all orientations. The reduction of surface recombination velocity (from PL data) was orientation dependent and especially pronounced for the case of (111)A and (111)B orientations. The effect of thin dielectric layers deposited on S-treated surfaces was also investigated, particularly for (100) and (111)A orientations. SPV data shows a strong increase in the above band gap signal after both Streatment and dielectric film deposition, which was higher than that measured for only S-treated surfaces. PR data showed an increase in the interfacial electric field following deposition of dielectric film. The results of absolute S-surface coverage measurements using particle-induced X-ray emission measurements were correlated with the optical characteristics.

Control of defect complex formation in thermally quenched semi-insulating GaAs using capless laser processing

The effect of Laser Processing (LP) on defect complex formation and dissociation in ITC-GaAs was investigated by Surface Photovoltage (SPV), Photoluminescence (PL) and C-V profiling measurements. We propose that the reduction in hole concentration on LP samples is caused by a complexing of CAs and a laser-induced primary point defect. A clear correlation was found between the introduction of this complex and sample characteristics: these include, enhanced SPV signals, reduced CAs related PL intensities and a nonuniform distribution of ionized acceptors. In this exploratory work, we have demonstrated the unique influence of LP on the distribution of isolated acceptors and the free carrier concentration.