Search

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.

The influence of (NH4)2S treatment on the surface properties of GaP is presented for the first time. Changes in the chemical composition and Fermi level position are characterized using X-ray photoelectron spectroscopy. These measurements show that after surface treatment, the GaP surface is free of native oxides. A strong enhancement (~ 50 times) in the cathodoluminescent efficiency was observed for sulfur passivated samples. Schottky diode characteristics were used to reveal changes in the barrier height and interface state density due to surface treatment. Changes in carrier concentration were also found to be reflected in measured Raman spectra. The passivation mechanism is also briefly discussed.

A photoluminescence study was made of the green emission band in GaP:Zn,O grown by liquid-phase epitaxy. The spectra are shown to originate from donor-acceptor-pair transitions involving sulfur and zinc. This conclusion is supported by an analysis of the peak energy, peak shape, excitation-intensity dependence of the spectrum, and secondary-ion-mass-spectrometry data. A series of three LO(\ensuremath{\Gamma}) phonon replicas are identified. Temperature-dependence measurements of the no-phonon donor-acceptor-pair peak and the Zn-O bound-exciton-complex peak intensities reveal the important role that green transitions play in reducing the recombination rate of the primary red recombination photoluminescence.

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.

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.

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.

Dual beam (bias and probe) transient Surface Photovoltage (SPV) measurements were made on undoped Semi-Insulating (SI) GaAs over an extended temperature range. Above 270 K, SPV recovery transients following a bias pulse were shown to reflect near surface conductivity changes; these are in turn controlled by surface/interface state thermal emission. Owing to the absence of a strong surface electric field in this material, the emitted carriers are not immediately removed from the near surface region. The recapturing of the emitted carriers is shown to be responsible for non-exponential conductivity and reciprocal-SPV transients. This behavior is considered to be characteristic of relaxation-type semiconductors with near-surface ungated structures. Below 150 K, the photoinduced transition of EL2 from its ground to metastable state EL2& was shown to change the effective electron and hole mobilities and augment the SPV signals immediately following the bias pulse. Thermally induced EL2& recovery above 120 K decreases the SPV signal from its maximum. This decay transient was analyzed and the decay rate fitted to a single exponential. An activation energy of 0.32 eV and a pre-exponential constant of 1. 9× 1012 s−1 were obtained, and attributed to the thermal recovery rate for EL2&.

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 (NH4)2S or S2Cl2 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.

We report on passivation of A1GaiAs/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 areduction 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 (O

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.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Tritium is a radioisotope that emits beta radiation on its decay with a half life exceeding twelve years. The average emitted beta particle energy is ~6 keV. Typically for a semiconductor with bandgap on the order of ~1-2 eV for example, one incident beta particle could result in the production of ~1000 electron-hole pairs in the semiconductor. Beta decay thus represents an interesting generation source for the design of semiconductor-based light sources requiring no external energy supply. In this work we study the luminescence mechanisms resulting from such excitation in materials from the GaInAsP alloy system.

A low-temperature spectrally resolved study was made of the decay characteristics of green emission in liquid-phase epitaxially grown GaP:Zn,O. An analysis of the steady-state and transient characteristics of this emission is shown to be consistent with a proposed model. The dependence of the pair transition rate on the donor-acceptor pair separation is discussed with reference to a theoretical model based upon the overlap of donor and acceptor wave functions within the effective-mass approximation. A previously reported value of 12.2 A for the zinc acceptor (shallow impurity) effective Bohr radius in GaP is confirmed

Presentation d'une nouvelle methode de croissance de HgCdTc a partir de solutions. Developpement d'un modele de cinetique de croissance utilise pour interpreter les variations de la vitesse de croissance, de l'epaisseur de couche et de la composition de surface avec le temps de croissance, le niveau de la solution et la pression appliquee

Infrared photovoltaic detectors (operating in the spectral range 8–14 μm) have been prepared as p−n junctions in epitaxial Hg( 1− x − y )Cd x Mn y Te layers. Measurements of their electric and photoelectric properties have been performed. The tunneling current has turned out to be the main component of the dark current in the temperature range 4.2–100 K, whereas for the higher temperature range, generation-recombination and diffusion currents have predominated.

Presentation de resultats sur la croissance de couches de HgCdTe par electroepitaxie a partir de solutions riches en tellure a 501°C

We report on the optical characterization of sulphur (S) passivated AlxGa1−xAs/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.