L. Hart

4-11 Mu-M Infrared-Emission and 300 K Light-Emitting-Diodes From Arsenic-Rich Inas1-Xsbx Strained-Layer Superlattices

Arsenic-rich InAs/lnAs1-xSbx strained layer superlattices (SLSs) grown on GaAs substrates by molecular beam epitaxy (MBE) are studied for their potential application as infrared emitters. The long-wavelength emission (4-11 mu m) is highly sensitive to superlattice design parameters and is accounted for by a large type-II band offset, greater than in previously studied antimony-rich InSb/lnAs1-xSbx SLSs. High internal PL efficiencies (>10%) and intense luminescence emission were observed at these long wavelengths despite large dislocation densities. Initial unoptimized InAs/lnAs1-xSbx SLS light emitting diodes gave approximately=200 nW of lambda =5 mu m emission at 300 K.

Native defects in low‐temperature GaAs and the effect of hydrogenation

A range of experimental techniques has been used to measure point defect concentrations in GaAs layers grown at low temperatures (250 °C) by molecular‐beam epitaxy (LT‐GaAs). The effects of doping on these concentrations has been investigated by studying samples containing shallow acceptors (Be) or shallow donors (Si) in concentrations of ∼1019 cm−3. Material grown under As‐rich conditions and doped with Be was completely compensated and the simultaneous detection of As0Ga by near‐band‐edge infrared absorption and As+Ga by electron paramagnetic resonance confirmed that the Fermi level was near the midgap position and that compensation was partly related to AsGa defects. There was no evidence for the incorporation of VGa in this layer from positron annihilation measurements. For LT‐GaAs grown under As‐rich conditions and doped with Si, more than 80% of the donors were compensated and the detection of SiGa–VGa pairs by infrared localized vibrational mode (LVM) spectroscopy indicated that compensating VGa de...

Efficient 300 K light-emitting diodes at λ∼5 and ∼8 μm from InAs/In(As1−xSbx) single quantum wells

300 K light-emitting diodes which emit at 5 and 8 μm with quasi-cw output powers of up to 50 and 24 μW, respectively, are reported. The devices have a single molecular beam epitaxy grown InAs/In(As, Sb) quantum well in the active region with a strong type-IIa band alignment giving mid-IR emission at energies up to 64% lower than the alloy band gap. The emission energies are shown to be in good agreement with a k⋅p bandstructure model where Qc, the ratio of the strained conduction-band offset to the band-gap difference between the two strained superlattice components, is found to be ∼2.0.

A MAGNETO-PHOTOLUMINESCENCE INVESTIGATION OF THE BAND OFFSET BETWEEN INAS AND ARSENIC-RICH INAS1-XSBX ALLOYS

InAs/InAs0.865Sb0.135 quantum wells are characterized using magneto‐photoluminescence. Band‐ to‐band transitions are found at energies lower than the band gaps of either the InAs or the InAs0.865Sb0.135 with photoluminescence emission at wavelengths up to 4.8 μm. By modeling the quantum size shifts of the photoluminescence transitions and their energy shift in a magnetic field, the valence band offset between InAs and In(As,Sb) is deduced to be type II with electron confinement in the In(As,Sb) alloy and hole confinement in InAs.

The strain relaxation of In0.1Ga0.9As on GaAs (110) grown by molecular beam epitaxy

The strain relaxation of In0.1Ga0.9As layers on GaAs (110) was studied by transmission electron microscopy (TEM) and x‐ray diffraction. TEM observation showed that strain relief in the (110) interface is initially dominated in the [001] direction by the formation of 60° type dislocations and stacking faults via {111}〈011〉 slip systems for layer thicknesses up to approximately 200 nm. As the layer thickness increases, {113}〈011〉 slip systems became active and the resultant misfit dislocations contribute strain relief in both [001] and [110] directions. The efficiency of strain relief by the different misfit dislocations is discussed.

The transition from dilute aluminum δ structures to an AlAs monolayer in GaAs and a comparison with Si δ doping

Superlattices of Al δ layers embedded in GaAs have been grown by molecular beam epitaxy at 400 °C on (001) GaAs. Infrared absorption measurements revealed a shift of the Al localized vibrational mode (LVM) from 361.4 to 358.3 cm−1 as the doping was increased from 0.25 monolayers (ML) to 1.4 ML per δ plane, while Raman scattering demonstrated a clear transition from the TO‐like LVM to a longitudinal LO‐like mode. X‐ray measurements showed that the Al atoms were confined to a thickness of 6 A for the highest areal concentrations. The LVM behavior is compared with that of Si δ layers where the absorption tends to zero as the areal concentration increases up to 0.5 ML. It is concluded that SiGa atoms move off their lattice sites and/or change their charge states as the coverage approaches 0.5 ML.

Carrier lifetime and exciton saturation in a strain-balanced InGaAs/InAsP multiple-quantum-well

The bleaching of the n = 1 heavy-hole and light-hole exciton absorption has been studied at room temperature and zero bias in a strain-balanced InGaAs/InAsP multiple quantum well. Pump-probe spectroscopy was used to measure the decay of the light-hole absorption saturation, giving a hole lifetime of only 280 ps. As only 16 meV separates the light- and heavy-hole bands, the short escape time can be explained by thermalization between these bands followed by thermionic emission over the heavy-hole barrier. The saturation density was estimated to be 1 × 1016 cm-3; this is much lower than expected for tensile-strained wells where both heavy and light holes have large in-plane masses.

ROOM-TEMPERATURE CHARACTERIZATION OF INGAAS/ALAS MULTIPLE QUANTUM WELL P-I-N DIODES

We report the growth and fabrication of strained InxGa1−xAs/AlAs multiple quantum well p‐i‐n diodes, where 5.6%<x<15.3%. Characterization via high‐resolution x‐ray diffraction shows that for the higher indium composition, partial relaxation of the strain has occurred. Using photocurrent spectroscopy, we demonstrate that all the samples studied (whether partially relaxed or not) show (i) strong room‐temperature excitonic features and (ii) under an applied electric field, a strong quantum confined Stark effect with retention of clearly resolvable excitons for fields up to ≊300 kV/cm. Both these results can be attributed to the substantial confining potential caused by our use of AlAs barriers. The results demonstrate that the system has potential use for the production of optical modulators.

Photoconductivity studies of InAsP/InP heterostructures in applied magnetic and electric fields

A series of compressively strained multiple quantum-well structures have been studied in magnetic fields up to 15 T and electric fields up to . Photoconductivity spectra have shown several well-defined transitions from the quantum-well region of the samples, allowing an accurate determination of the parameters of this system. These parameters give a convincing description of photoconductivity spectra obtained with an applied magnetic field, in which Landau levels were clearly resolved, giving information about the in-plane masses and excitonic binding energies; and with an external electric field in both forward and reverse biases.

Si delta -doping in GaAs: investigation of the degree of confinement and the effects of post-growth annealing

A stack of 60 delta -planes, each containing a Si areal concentration of 3.4*1014 cm-2 ( approximately 0.5 monolayers, ML), grown in GaAs by molecular beam epitaxy at 400 degrees C has been examined before and after post-growth annealing by high-resolution X-ray diffractometry, transmission electron microscopy, secondary-ion mass spectrometry and infrared absorption localized vibrational mode (LVM) spectroscopy. These techniques provided complementary information concerning the concentration, spatial distribution and site occupancy of the Si atoms. It was found for the as-grown samples that the Si was located on Ga lattice sites (SiGa) and confined to layers no more than 2 ML in thickness. Annealing at 600 degrees C resulted in spreading of the delta -layers, with some Si remaining on the original planes, and the remainder diffusing away, resulting in a Si concentration of 2.1*1019 cm-3 between the delta -planes. LVM spectroscopy indicated that the diffused Si atoms were present as SiGa donors, SiAs acceptors, SiGa-SiAs pairs and Si-X complexes. After the samples were annealed at 800 degrees C or 950 degrees C only a uniform Si concentration of 3*1019 cm-3 was detected, although there was excess Si in the surface region where dislocation loops were observed. It is concluded that there is a maximum silicon concentration in solution that is in equilibrium with the delta -layers at 600 degrees C and that the Si in the delta -layers is present as dimers or larger 2D clusters.