Qingqing Xu

Studies on InAs/GaSb superlattice structural properties by high resolution x-ray diffraction

This paper presents work on InAs/GaSb superlattice structural property studies. The superlattice materials were grown by molecular beam epitaxy and measured by high resolution x-ray diffraction, and measured x-ray rocking curves were fitted to the simulated ones in order to fully analyze the superlattice structures. A four-layer model including an InAs layer, a GaSb layer and two interface layers was used for simulation. The results show that the two interface layers are ternary compounds of InSbAs, which have, respectively, an Sb composition of 0.99 at the InAs-on-GaSb interfaces and an Sb composition of 0.01 at the GaSb-on-InAs interfaces. This is the first article, to our knowledge, on the detailed analysis of the InAs/GaSb superlattice interface structures. The experiments also demonstrate that the As flux during the epitaxy growth affects the interface layer InSbAs compositions and hence the lattice mismatch between the superlattices and the substrates. With an As beam equivalent pressure change from...

Evolution of interfacial properties with annealing in InAs/GaSb superlattice probed by infrared photoluminescence

Postgrowth rapid-annealing effects are investigated by infrared photoluminescence (PL) in the InAs/GaSb type-II superlattice (T2SL) with intentional InSb interfaces. The changes in PL energy, linewidth, and integral intensity with temperature indicate that the PL process is dominated by electron–phonon interaction in the InSb-like interfaces and adjacent narrow portions of InAs layers. The interfacial electron level serves as a thermal escape channel for the first miniband electrons and affects the T2SL high-temperature properties. Annealing promotes the interfacial atom exchange and changes the electron thermal escape energy. It transforms the PL-related interfacial regions to InSb1−xAsx at annealing temperatures below 470 °C, activates In/Ga exchange, and transforms the regions to In1−yGaySb at 500 °C. The results indicate that an optimized annealing temperature is crucial for improving the T2SL performance by postgrowth annealing, and infrared PL can serve as an effective criterion for the optimization.

Growth and fabrication of InAs/GaSb type II superlattice mid-wavelength infrared photodetectors

AbstractWe report our recent work on the growth and fabrication of InAs/GaSb type II superlattice photodiode detectors. The superlattice consists of 9 monolayer InAs/12 monolayer GaSb in each period. Lattice mismatch between the GaSb substrate and the superlattice is 1.5 × 10-4. The full width at half maximum of the first-order satellite peak from X-ray diffraction is 28 arc sec. The P-I-N photodiodes in which the absorption regions (I regions) have 600 periods of superlattice show a 50% cutoff wavelength of 4.3 μm. The current responsivity was measured at 0.48 A/W from blackbody radiation. The peak detectivity of 1.75 × 1011 cmHz1/2/W and the quantum efficiency of 41% at 3.6 μm were obtained. PACS: 85.60.-q; 85.60.Gz; 85.35.-Be.

Dark current analysis of long wavelength InAs/GaSb superlattice infrared detector

Dark current characteristics of long wavelength InAs/GaSb superlattice (SL) detectors have been studied in this paper. The long wavelength SL structure consists of periodic 14 monolayers (MLs) InAs and 7 MLs GaSb with 50% cutoff wavelength around 11 μm. Three InAs/GaSb superlattice detectors of PBIN structure were grown at different temperatures. Wet chemical etching was used to define device mesa. SiO2 was used for device passivation to suppress the sidewall leakage current. Electron barriers were inserted between the absorber region and P-type conducting region to reduce the bulk dark current. The detectors grown at 380oC have the lowest dark current densities as 0.01A/cm2 and the best R0A value as 13 Ωcm2. We simulated four main dark current mechanisms. The result shows that the intrinsic carrier density is extracted to be 3.5E15 cm-3 which matches the C-V measurement very well. And the GR and trap assisted tunnel current dominate the dark current of the device due to the large trap densities and short GR lifetimes.

Interface design and properties in InAs/GaSb type-II superlattices grown by molecular beam epitaxy

In this paper we reported our systematic studies on InSb interface growth in InAs/GaSb SLs structure. Two typical interfaces growth mode, migration-enhanced epitaxy (MEE) and conventional molecular beam epitaxy (MBE), were designed for the 12 ML InAs/12 ML GaSb SLs material and the detail properties were discussion by the experimental measurement and simulation analysis. Our results indicated that the surface of SLs sample with the InSb interface layers grown by MEE method shows smaller RMS both on the 2 μm x 2 μm and 50 μm x 50 μm scan area by AFM measurement, and its PL intensity is about 1.3 times stronger than that of SLs sample grown by MBE. Besides, the MEE samples had significant As composition in InSb interface layers which was extracted by the HRXRD fitting.

X-ray diffraction analysis of high quality InAs/GaSb Type II superlattices grown by MBE

High resolution X-ray diffraction is used to study InAs/GaSb superlattices structural properties. The SL materials were grown by molecular beam epitaxy on the GaSb substrates. We optimize the shutter sequences and soak time to improve the SL interface and the material quality. The reciprocal space maps show that the materials are almost fully stained. The angle distance between the zeroth order SL peak and the substrate in ω - 2θ spectrum is about 10 arcsec. The full-width half-maximum (FWHM) of the zeroth order SL peak is 25 arcsec. Using a four layer model including two InSb interfaces, we simulated the scanning curve and found there is different layer formed in InAs-on-GaSb and GaSb-on-InAs interfaces. The arsenic pressure and the interface structure are optimized to get better material quality for long wavelength SL samples. With optimized growth condition and suitable InSb-like interface structure, high quality SL samples for both mid and long wavelength range are fabricated. The average roughness from AFM on a 2×2 um2 scan area is less than 1.5 angstrom.

Electrical and optical performances of InGaAs/GaAsSb superlattice short-wavelength infrared detectors

Abstract. We report on a p-i-n photodetector based on type II InGaAs/GaAsSb SLs with a cutoff wavelength of 2.5  μm at room temperature. High quality materials were grown on an n-type (100) InP substrate by molecular beam epitaxy. Photoluminescence spectroscopy peak of the SLs around 2.5  μm and atomic steps in the atomic force microscope image were clearly observed. A device with the 100% cutoff wavelength of 2.5  μm at 293 K was fabricated. Temperature-dependent current-voltage measurements show that the diffusion current and generation-recombination current dominate at temperatures higher than 200 K while the generation-recombination current and trap-assisted tunneling current dominate at temperatures below 200 K. The optical response measurement quantum efficiency increases with reverse bias, and a diffusion length of 0.3  μm was extracted. The cause of the small diffusion length and possible approaches to improve it were briefly discussed.

Short-wavelength infrared photodetector with InGaAs/GaAsSb superlattice

In this paper, our recent study on InGaAs/GaAsSb Type II photodetector for extended short wavelength infrared detection is reported. The high quality InGaAs/GaAsSb superlattices (SLs) was grown successfully by molecular beam epitaxy. The full width of half maximum of the SLs peak is 39”. Its optical properties were characterized by photoluminescence (PL) at different temperature. The dependences of peak energy on temperature were measured and analyzed. The photodetector with InGaAs/GaAsSb absorption regions has a Quantum Efficiency (QE) product of 12.51% at 2.1um and the 100% cutoff wavelength is at 2.5um, at 300K under zero bias. The dominant mechanism of the dark current is discussed.

The accurate measurement of background carrier concentration in short-period longwave InAs/GaSb superlattices on GaSb substrate

In the paper we report on a technology of removing the conducting GaSb substrate with the mechanical thinning and wet etch, and then the electrical measurement of non-intentionally doped long-wavelength Infrared (LWIR) type-II InAs/GaSb superlattices (SLs). The SL structures were made of periodic 15 InAs monolayers (MLs) and 7 GaSb MLs with cutoff wavelengths around 11 μm. A etch stop layer was grown between the GaSb substrate and SL for substrate removal for no chemical solution exists with enough selectivity between the GbSb and SLs during the wet etch process. After removing the GaSb substrate, the transport properties measurements of SLs are performed using temperature dependent from 20 k to 296 k and variable magnetic field Hall measurements. It is found that the LWIR SLs is n-type at the all temperatures. Meanwhile, from the result of the mobility spectrum analysis at 76 k, there are more than one type carrier conducting in the LWIR SLs material.