ALBERT

Notes: Growth of GaxIn1−xAsyP1−y was performed on (001) InP by molecular-beam epitaxy employing solid phosphorus and arsenic valved sources. Relative anion incorporation rates were found strongly dependent upon the Ga mole fraction, growth temperature, and incident As and P beam fluxes. The relative incorporation of As and P can be predicted from the ratio of the square of the incident column-V fluxes. Although the As anion always incorporated preferentially into the lattice, significant enhancement in P incorporation was observed as growth temperature and Ga mole fraction increased. Strong spinoidal decomposition and a temperature-dependent surface morphology was found for lattice-matched compositions having peak photoluminescence emission wavelengths between 1.25 and 1.36 μm. Heterojunction laser diodes utilizing different GaxIn1−xAsyP1−y active regions were fabricated with emission ranging from 1.21 to 1.53 μm. The best broad area threshold current density obtained for a 500 μm cavity length was 1.7 kA/cm2 with a maximum two facet slope efficiency of 0.24 W/A, which is comparable to the state-of-art performance. © 1996 American Institute of Physics.

Notes: We describe vertical cavity surface emitting lasers of GaAs active regions (0.7 μm thick) emitting at 0.85 μm and of In0.1Ga0.9As-GaAs active regions emitting at 0.90 μm. The vertical cavity is formed using an AlxGa1−xAs-AlAs quarter-wave stack as the n-type mirror and the metal Ag as the p-type mirror. The Ag mirror has potential for reduced series resistance, reduced thermal resistance, and more simplified device processing over other mirror structures for vertical cavity laser diodes. Current thresholds for pulsed room-temperature operation as low as 16 kA/cm2 for the GaAs and 51 kA/cm2 for the In0.1Ga0.9As-GaAs devices have been measured.

Notes: Two-terminal switching action is observed in a new optoelectronic device structure. The device has a high-impedance state without light emission and a low-impedance state characterized by strong spontaneous emission. The transition from either state to the other may be induced by the appropriate optical or electrical input. It is clear that with the appropriate optical cavity construction the switching device will operate as a laser in the on state rather than in the spontaneous mode reported here. In principle, the device offers large digital optical gain determined by its optical sensitivity and its maximum output power.

Notes: Pressure-tuned resonance Raman scattering (RRS) experiments in Ga1−xInxAs/Ga1−yAlyAs strained-layer quantum-well samples with x=0.15 and y=0.15, on a GaAs substrate, are reported. The photoluminescence (PL), 2LO-, and LO-phonon Raman-scattered intensities were followed as a function of pressure using the diamond cell. In backscattering geometry and with (100) samples, three sharply defined 2LO-phonon resonances are observed, at 2.1, 3.8, and 5.2 GPa, with 647.1-nm excitation ((h-dash-bar)ωL=1.916 eV), and these are identified to be from the AlGaAs, GaAs, and InGaAs layers, respectively. At the above pressures, the 2LO peak of the layer falls right on top of the PL peak of the corresponding layer, revealing that the resonance occurs when E0=(h-dash-bar)ωS (2LO). For the LO-phonon intensity, maxima are observed at 2.8 and 4.7 GPa, respectively, from the AlGaAs layer and GaAs substrate. While the LO-resonance profile (pressure versus phonon intensity) for the AlGaAs layer is narrow, the profile of the GaAs substrate layer is highly asymmetric. The InGaAs LO-resonance is totally masked by the strong GaAs LO phonon. The pressure dependence of the E0 gap, determined from PL data, reveals that the resonance condition for 2LO is E0=(h-dash-bar)ωS (2LO) and, for LO, E0=(h-dash-bar)ωL. Results with samples of different Al content and (h-dash-bar)ωL are consistent with the above conditions. A brief discussion of the theory of the RRS cross section is given, and it is suggested that the observed 2LO-resonance scattering is dominated by Frölich interaction, and that it could be a double resonance. The asymmetry in the LO resonance of the GaAs substrate, we believe, is due to the pressure-induced transparency, and this is a problem when dealing with pressure-tuned RRS, in multiple-quantum-well structure with GaAs or AlGaAs substrates. The usefulness of the 2LO resonance in locating the E0 gap is indicated, and the indistinguishability between luminescence and Raman scattering at the center of the 2LO resonance is pointed out. The need to study photoluminescence and Raman scattering in pressure-tuned RRS experiments is emphasized.

Notes: The realization of collector-up light-emitting complementary charge injection transistors is reported. The devices have been implemented in molecular-beam-epitaxy-grown n-InGaAs/InAlAs/p-InGaAs and n-InGaAs/InP/p-InGaAs heterostructures using a self-aligned process for the collector stripe definition. Electrons, injected over the wide-gap heterostructure barrier (InAlAs or InP) by the real-space transfer (RST) process, luminesce in the low-doped p-type InGaAs active layer. An essential feature of present devices, besides their self-aligned collector-up configuration, is a relatively heavy doping of the n-type emitter channel, with the sheet dopant concentration of 4×1012 cm−2. This ensures a higher uniformity of the electric field in the channel and provides a relief from RST instabilities at a high level of collector current (linear density ∼10 A/cm). Devices with InAlAs and InP barriers show rather different optical characteristics, mainly due to the different band lineups ΔEC/ΔEV in InGaAs/InAlAs and InGaAs/InP heterostructures, leading to different ratios between the RST current and the parasitic leakage of holes from the collector into the channel. At high RST current densities, the effective carrier temperature Te in the active collector layer, determined from the high-energy tails of the luminescence spectra, is strongly enhanced compared to the lattice temperature. This decreases the device radiative efficiency and leads to a thermionic emission of carriers out of the active layer.

Notes: We propose and study a new GaSb/InAs/GaSb/AlSb/InAs broken-gap interband tunneling diode by varying the thicknesses of the InAs layer. A twice-higher peak current density and a three-times-higher peak-to-valley current ratio in the proposed structure with a 30-A(ring)-thick InAs layer were observed relative to the structure with no InAs layer. This result indicates that the characteristic of the negative differential resistance can be improved simply by placing a thin effective InAs barrier on the GaSb side of the GaSb/AlSb/InAs single-barrier structure. The increase of the peak current is interpreted as the result of forming a quasi-bound state in the GaSb well. This interpretation is supported by the observation that the current-voltage characteristic of the proposed structure is similar to that of a conventional GaSb/AlSb/GaSb/AlSb/InAs double-barrier interband tunneling structure.

Notes: Au, Cu, Ag, and Al are deposited on Te-doped n-GaSb layers directly grown on lattice mismatched GaAs semi-insulating substrates. Sb4/Ga beam equivalent pressure ratios are found to profoundly influence the electrical properties of the Schottky diodes investigated here. The fact that both breakdown voltage and barrier height decrease with increasing Sb4/Ga ratios is attributed to the increase in surface state densities for samples grown at higher Sb4/Ga ratios. This suggestion is further confirmed by the model of surface state densities employing the relationship of barrier height to metal work function. The surface state densities are in the range of 2.3×1014 to 1.2×1015 states/cm2/eV corresponding to Sb4/Ga ratios of 2 to 9, respectively. X-ray rocking peaks of samples grown at various Sb4/Ga ratios, and subsequently subjected to annealing, indicate different interactions at the interfaces which might support the observations.

Notes: We investigated interband tunneling transport through a hole well in five GaSb/AlSb/GaSb/AlSb/InAs type II tunnel devices in which the effect of the variation of barrier and well widths is systematically studied. Low temperature measurements were performed using high magnetic fields applied perpendicular to the current and hydrostatic pressures as external perturbations. A resonant current through the ground heavy hole subband in the GaSb well could be identified for the first time. This examination points out (i) the role of in-plane momentum conservation in determining the resonance onset voltage, and (ii) the occurrence of a shoulder in the current when a maximum of states conducts through a resonant subband.

Notes: The high-speed modulation characteristics of ridge waveguide InGaAs/GaAs strained quantum well lasers have been investigated. The lasers have bandwidth of 12 GHz at 21 mW of output power. The differential gain coefficient, the nonlinear damping factor (κ factor) and the gain suppression coefficient (ε) are found to be 6.4 × 10−16 cm2, 0.6 ns and 6.2 × 10−17 cm3, respectively. The above differential gain coefficient and κ factor for InGaAs/GaAs strained quantum-well lasers are a factor of 2 larger than that for unstrained InGaAs/InP quantum-well lasers. The ε value for these strained and unstrained quantum-well lasers are comparable.