D. Donetsky

Carrier lifetime measurements in short-period InAs/GaSb strained-layer superlattice structures

Minority carrier lifetime and interband absorption in midinfrared range of spectra were measured in InAs/GaSb strained-layer superlattices (SLSs) grown by molecular beam epitaxy on GaSb substrates. The carrier lifetime in 200-period undoped 7 ML InAs/8 ML GaSb SLS with AlSb carrier confinement layers was determined by time-resolved photoluminescence (PL) and from analysis of PL response to sinwave-modulated excitation. Study of PL kinetics in frequency domain allowed for direct lifetime measurements with the excess carrier concentration level of 3.5×1015 cm−3. The minority carrier lifetime of 80 ns at T=77 K was obtained from dependence of the carrier lifetime on excitation power.

Minority carrier lifetime in type-2 InAs–GaSb strained-layer superlattices and bulk HgCdTe materials

Minority carrier lifetime, τ, in type-2 strained-layer superlattices (SLSs) and in long-wave Hg0.78Cd0.22Te (MCT) was measured by optical modulation response technique. It was shown that at 77 K radiative recombination can contribute to the measured τ values. The Shockley–Read–Hall (SRH) lifetimes were attained as 100 ns, 31 ns, and more than 1 μs for midwave infrared superlattices, long-wave infrared (LWIR) superlattices, and MCT correspondingly. The nature of the difference between the SRH lifetimes in LWIR superlattice and MCT is discussed.

High power 2.4μm heavily strained type-I quantum well GaSb-based diode lasers with more than 1W of continuous wave output power and a maximum power-conversion efficiency of 17.5%

The authors demonstrate a double quantum well GaSb-based diode laser operating at 2.4μm with a room-temperature cw output power of 1050mW and a maximum power-conversion efficiency of 17.5%. Laser differential gain with respect to current increases by a factor of 2 and laser threshold current is nearly halved when the compressive strain in the quantum wells is increased from 1.2% to 1.6%. This improvement is due to substantially improved hole confinement in the heavily compressively strained active region.

Role of p-doping profile and regrowth on the static characteristics of 1.3-/spl mu/m MQW InGaAsP-InP lasers: experiment and modeling

In this paper, we study both experimentally and theoretically how the change of the p-doping profile, particularly the p-i junction placement, affects the output characteristics of 1.3-/spl mu/m InGaAsP-InP multiple-quantum-well (MQW) lasers. The relationship between the p-doping profile before and after regrowth is established, and the subsequent impact of changes in the p-i junction placement on the device output characteristics, is demonstrated. Device characteristics are simulated including carrier transport, capture of carriers into the quantum wells, the quantum mechanical calculation of the properties of the wells, and the solution for the optical mode and its population self-consistently as a function of diode bias. The simulations predict and the experiments confirm that an optimum p-i junction placement simultaneously maximizes external efficiency and minimizes threshold current. Tuning of the base epitaxial growth Zn profile allows one to fabricate MQW devices with a threshold current of approximately 80 A/cm/sup 2/ per well for devices with nine QWs at room temperature or lasers with a characteristic temperature T/sub 0/=70 K within the temperature range of 20/spl deg/C-80/spl deg/C.

Properties of unrelaxed InAs1−XSbX alloys grown on compositionally graded buffers

Unrelaxed InAs1−xSbx layers with lattice constants up to 2.1% larger than that of GaSb substrates were grown by molecular beam epitaxy on GaInSb and AlGaInSb compositionally graded buffer layers. The topmost section of the buffers was unrelaxed but strained. The in-plane lattice constant of the top buffer layer was grown to be equal to the lattice constant of unrelaxed and unstrained InAs1−xSbx with given X. The InAs0.56Sb0.44 layers demonstrate photoluminescence peak at 9.4 μm at 150 K. The minority carrier lifetime measured at 77 K for InAs0.8Sb0.2 was τ = 250 ns.

Molecular beam epitaxy control and photoluminescence properties of InAsBi

Thick InAsBi layers were grown for photoluminescence (PL) characterization. The As to In overpressure ratio was carefully characterized and adjusted to achieve Bi-droplet-free surfaces. A closed loop feedback system was used to maintain the As overpressure during a 5-h deposition sequence. Despite a high degree of control of the growth parameters, evidence for local phase separation was observed in the PL spectra.

Metamorphic InAsSb/AlInAsSb heterostructures for optoelectronic applications

Metamorphic heterostructures containing bulk InAs1−xSbx layers and AlInAsSb barriers were grown on GaSb substrates. The lattice mismatch (up to 2.1%) between the GaSb substrates and the InAsSb layers was accommodated by the growth of GaInSb linearly graded buffers. The 1 μm thick InAsSb0.44 layer with an absorption edge above 9 μm exhibited an in-plane residual strain of about 0.08%. InAs1−xSbx structures with x = 0.2 and x = 0.44 operated as light emitting diodes at 80 K demonstrated output powers of 90 μW and 8 μW at 5 μm and 8 μm, respectively.

Effects of carrier concentration and phonon energy on carrier lifetime in Type-2 SLS and properties of InAs 1-X Sb X alloys

GaInSb and AlGaInSb compositionally graded buffer layers grown on GaSb by MBE were used to develop unrelaxed InAs1-XSbXepilayers with lattice constants up to 2.1 % larger than that of GaSb. The InAsSb buffer layer was used to grow InAs0.12Sb0.88 layer on InSb. The structural and optical characterization of 1-μm thick InAs1-xSbx layers was performed together with measurements of the carrier lifetime.

Reduction of interfacial recombination in GaInAsSb'GaSb double heterostructures

Minority carrier lifetimes in 0.55 eV band-gap GaInAsSb epitaxial layers that are double capped with GaSb or AlGaAsSb layers were determined using time-resolved photoluminescence. It was found that accumulation of electrons at the p-doped GaInAsSb/GaSb type-II interface contributes significantly to the interfacial recombination velocity S, which was measured to be 3100 cm/s. The use of heavily p-doped GaSb cap layers was proposed to eliminate the potential well of electrons and barrier for holes at the interface. Increasing the GaSb cap doping level from 1×1016 to 2×1018 cm−3 resulted in a 2.7 times reduction of S down to 1140 cm/s. The smallest value of S was determined to be 720 cm/s, which was obtained for structures with AlGaAsSb cap layers that have no valence band offset.

Effect of heterobarrier leakage on the performance of high-power 1.5 μm InGaAsP multiple-quantum-well lasers

Broad stripe 1.5 μm InGaAsP/InP multiple-quantum-well graded-index separate-confinement heterostructure lasers with different waveguide widths and doping profiles were designed, fabricated, and characterized. A record value of more than 16 W of pulsed optical power was obtained from lasers with a broadened waveguide design. Studies of the characteristics of lasers with different p-doping profiles as well as modeling data show that the heterobarrier electron leakage is responsible for the effect of the device optical power saturation with current.