P. J. P. Tang

SUPPRESSION OF AUGER RECOMBINATION IN ARSENIC-RICH INAS1-XSBX STRAINED LAYER SUPERLATTICES

Room-temperature pump-probe transmission experiments have been performed on an arsenic-rich InAs/InAs1-xSbx strained layer superlattice (SLS) above the fundamental absorption edge near 10 mu m, using a ps far-infrared free-electron laser. Measurements show complete bleaching at the excitation frequency, with recovery times which are found to be strongly dependent on the pump photon energy. At high excited carrier densities, corresponding to high photon energy and interband absorption coefficient, the recombination is dominated by Auger processes, A direct comparison with identical measurements on epilayers of InSb, of comparable room-temperature band gap, shows that the Auger processes have been substantially suppressed in the superlattice case as a result of both the quantum confinement and strain splittings in the SLS structure, In the nondegenerate regime, where the Auger lifetime scales as tau(aug)(-1)=C1Ne2, a value of C-1 some 100 times smaller is obtained for the SLS structure. The results have been interpreted in terms of an 8x8 k . p SLS energy band calculation, including the full dispersion for both k in plane and k parallel to the growth direction. This is the strongest example of room-temperature Auger suppression observed to date for these long-wavelength SLS alloy compositions and implies that these SLS materials may be attractive for applications as room-temperature mid-IR diode lasers

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.

Excitonic photoluminescence in high-purity InAs MBE epilayers on GaAs substrates

Temperature- and excitation-dependent photoluminescence measurements have been carried out on 0.7-5 mu m thick heteroepitaxial InAs layers grown by molecular beam epitaxy (MBE). Excitonic photoluminescence with linewidths down to 5 meV reveals the high optical quality of the epilayers despite the 7% mismatch between the InAs and the GaAs substrates. Peaks at 403 and 391 meV, which quench rapidly with increasing temperature, are attributed to bound excitons, and a sharp (7 meV FWHM) intense line at 417 meV is tentatively attributed to free excitonic recombination. A broad 18 meV wide band (peaking at 378 meV) which blue shifts with increasing excitation, characteristic of a donor-acceptor pair transition band, is reported for the first time in InAs.

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.

Optical studies of InAs/In(As,Sb) single quantum well (SQW) and strained-layer superlattice (SLS) LEDs for the mid-infrared (MIR) region

We report on electroluminescence and photoluminescence studies of arsenic rich InAs1-xSbx heterostructure LEDs for the MIR region. Single-quantum- well LEDs have demonstrated 300 K of approximately 24 (mu) W and approximately 50 (mu) W and approximately 8 micrometers , respectively, with corresponding internal quantum efficiencies of 0.8% and 1.6%. We also demonstrate 4.2 micrometers , 300 K emission from strained-layer superlattice (SLS) LEDs with AlSb electron confining barriers with output powers > 0.1 mW. In reverse bias, these SLS devices exhibit negative luminescence efficiencies of approximately 14% at 310 K.

The evaluation and control of quantum wells and superlattices of III–V narrow gap semiconductors

The growth and evaluation of InAs/GaSb/AlSb quantum wells and InAs, -,Sb,/InAs strained layer superlattices are discussed. A characteristic of the InAs/GaSb/AISb combinations is their high mobility and the applications are mainly concerned with optimising the mobility. The InAs, _ ,

Photoluminescence studies of n-i-p-i superlattices in InSb and InAs: suppression of Auger recombination due to type II potentials

b,/InAs strained-layer superlattices have rather long non-radiative lifetimes despite inferior structural quaIity, as demonstrated by time-resolved pump-probe measurements with a free electron laser. Q 1997 Published by Elsevier Science S.A.

Photo- and electro-luminescence studies of uncooled arsenic-rich In(As,Sb) strained layer superlattice light-emitting diodes for the 4-12-μm band

Infrared photoluminescence (PL) from InAs and InSb n-i-p-i superlattices grown by MBE has been found for the first time and has been studied over an extended temperature range. Quantum confined band-to-band transitions are observed at lambda approximately 6.5 mu m and lambda approximately 12 mu m for an InSb n-i-p-i and lambda approximately 3.6 mu m for an InAs n-i-p-i, representing a reduction of more than 50% and 20% from the bulk bandgap values respectively. A blue shift of 20 meV in the effective bandgap of the InSb n-i-p-i is observed on increasing the excitation from 0.3 W cm-2 to 1.6 W cm-2. In contrast to bulk narrow-gap samples, the n-i-p-i luminescence conversion efficiency is remarkably stable against the effects of increasing temperature (only a twofold decrease between 14 and 77 K) and this is attributed to the suppression of the dominant Auger recombination mechanism by the type II n-i-p-i band structure.

Room Temperature led's for the MID-Infrared Based on in(AS,SB) Strained Layer Superlattices

4-12 micrometers Photoluminescence (PL) and electroluminescence (EL) at room temperature are observed from In(As,Sb) undoped strained layer superlattices (SLSs) and SLS diodes. The SLSs are grown by molecular beam epitaxy on GaAs substrates and are composed of arsenic rich alloys clad between InAs layers. The long wavelength emission is accounted for by an extreme type II valence band offset equals 830x meV (where x in the Sb composition). Internal PL efficiencies greater than 10% for light emission up to 9 micrometers are observed at 12 K in spite of presumed large dislocation densities due to the epilayer/substrate mismatch (approximately 7%). This is consistent with the thesis that defects in As rich alloys are, as in InAs, resonant with the conduction band instead of forming non-radiative recombination centers in the band gap. The high radiative efficiencies even at room temperature are attributed to the suppression of Auger recombination in the type II superlattice. We report the first Electroluminescence spectra covering the 4 - 12 micrometers wavelength range from a series of uncooled SLS LEDs. Clear atmospheric absorption features in the EL spectra demonstrate their usefulness for gas sensing applications. The growth of these devices on GaAs substrates offers the possibility of easy integration with existing III-V fabrication technologies.

BAND ALIGNMENTS AND OFFSETS IN IN(AS,SB)INAS SUPERLATTICES

Arsenic-rich InAs/InAs 1−x Sb x strained-layer superlattices (SLSs) are studied in time-resolved optical, and CW magneto-optical spectroscopies. A pronounced type-II offset, with electrons confined to the alloy layers, is found. High radiative efficiencies at wavelengths well into the mid-IR, and the suppression of Auger recombination yield LEDs operating at 3–10 μm. Present room temperature powers are ∼30 μW, probably limited by inadequate carrier confinement.