Yueming Qiu

Interband cascade infrared photodetectors with enhanced electron barriers and p-type superlattice absorbers

We present results on the optical and electrical performance of mid-infrared detectors based on interband-cascade structures. These devices include enhanced electron barriers, designed to suppress intraband-tunneling current between stages, and p-doped type-II InAs/GaSb superlattice absorbers. Within the sample set, we examined devices with different absorber thicknesses and doping levels. Carriers are extracted less efficiently in devices with longer absorbers, which is attributed to more band bending within the absorber due to electric charge accumulation. Also, devices with lower-doped (1u2009×u20091017 cm−3) absorbers are found to have better optical and electrical performances than those with higher levels of doping (3u2009×u20091017 cm−3). The overall performance of these devices was superior to previously reported results, with Johnson-noise limited detectivities, at 4.0 μm, as high as 6.0u2009×u20091012 and 2.5u2009×u20091011 Jones at 80 and 150 K, respectively.

Optical gain, loss, and transparency current in high performance mid-infrared interband cascade lasers

The net modal gain, optical loss, and transparency current of high-performance, narrow ridge waveguide interband cascade (IC) lasers have been measured using the Hakki–Paoli technique in the temperature range from T=78 to 270 K. In this temperature range, the optical loss of IC lasers increases from αw≈17u2009cm−1 at T=78u2009K to αw≈35 at T=270u2009K, the transparency current density rises from Itr=10 to 330u2009A∕cm2, and the differential gain decreases from gd≈2.2u2009cm∕A to gd≈0.06u2009cm∕A with a characteristic temperature of T0=130u2009K. The implications of these observed characteristics for IC lasers are discussed.

Bipolar cascade lasers with quantum well tunnel junctions

Bipolar cascade lasers with quantum wells (QWs) in tunnel junctions are proposed and demonstrated with emission wavelength near 2 μm based on an InGaAs/InP material system. These bipolar cascade lasers with QW tunnel junctions exhibited superior performance characteristics such as significantly reduced threshold voltage, increased quantum efficiency (>100%) and operation temperature over similar lasers without a QW in the tunnel junction. These broad-area lasers operated at temperatures up to 240 K in continuous wave mode and up to room temperature in pulsed mode.

Size-dependent scaling of exchange bias in NiFe2O4/NiO nanogranular systems synthesized by a phase separation method

Exchange bias (EB) effect has been studied in a series of nanogranular systems of ferrimagnetic (FiM) NiFe2O4 nanoparticles embedded into antiferromagnetic (AFM) NiO matrix, synthesized by a phase pprecipitation method from diluted Ni(1−x)FexO3 (xu2009=u20090.09) oxides. For these systems, the crystalline size (DNFO) of NiFe2O4 ranging from ∼3u2009nm to ∼55u2009nm has been obtained with thermal treated at different temperatures from 550u2009°C to 1000u2009°C. Magnetization measurement shows that both exchange bias field (HEB) and vertical magnetization shifts (MShift) can be exhibited below 250u2009K after field cooling procedure. The HEB and MShift decrease monotonically with crystalline size, and their behavior strongly depend on the crystalline size of NiFe2O4 nanoparticles. Linear relationship between HEB and MShift is observed for systems with smaller sizes (DNFOu2009≤u20098u2009nm), reveals a straightforward correlation between them. This phenomenon is ascribed to the interfacial exchange coupling between FiM NiFe2O4 clusters and spin-gla...

Temperature-dependent minority carrier lifetimes of InAs/InAs 1-x Sb x type-II superlattices

Temperature-dependent minority carrier lifetimes of InAs/InAs1-xSbx type-II superlattices are presented. The longest lifetime at 11 K is 504 ± 40 ns and at 77 K is 412 ± 25 ns. Samples with long periods and small wave function overlaps have both non-radiative and radiative recombination mechanisms apparent, with comparable contributions from both near 77 K, and radiative recombination dominating at low temperatures. Samples with short periods and large wave function overlaps have radiative recombination dominating from 10 K until ~200 K. The improved lifetimes observed will enable long minority carrier lifetime superlattices to be designed for high quantum efficiency, low dark current infrared detectors.

High-temperature operation of interband cascade infrared photodetectors with cutoff wavelengths near 8 μm

Abstract. We present our recent studies on a set of three different type-II InAs/GaSb superlattice interband cascade infrared (IR) photodetectors. Electroluminescence and x-ray diffraction measurements suggest that all the grown structures had comparable material qualities. Two of these detectors were two- and three-stage structures with regular-illumination configurations and the other was a two-stage structure with a reverse-illumination configuration. The 100% cutoff wavelength for these detectors was 6.2u2009u2009μm at 78 K, extending to 8u2009u2009μm at 300 K. At T=125u2009u2009K and higher temperatures, we were able to observe the benefits of the three-stage detector over the two-stage device in terms of lower dark current and higher detectivity. We conjecture that the imperfections from the device growth and fabrication had a substantial effect on the low-temperature device performance and were responsible for the unexpected behavior at these temperatures. We also found that the zero-bias photoresponse increased with temperatures up to 200 K, which was indicative of efficient collection of photogenerated carriers at high temperatures. These detectors were able to operate at temperatures up to 340 K with a cutoff wavelength longer than 8u2009u2009μm. This demonstrates the advantage of the interband cascade structures to achieve high-temperature operation for long-wave IR photodetectors.

Study of the valence band offsets between InAs and InAs1-xSbx alloys

InAs/InAs1-xSbx strain-balanced superlattices (SLs) on GaSb are a viable alternative to the well-studied InAs/Ga1-xInxSb SLs for mid- and long-wavelength infrared (MWIR and LWIR) laser and photodetector applications, but the InAs/InAs1-xSbx SLs are not as thoroughly investigated. Therefore, the valence band offset between InAs and InAs/InAs1-xSbx, a critical parameter necessary to predict the SL bandgap, must be further examined to produce InAs/InAs1-xSbx SLs for devices operational at MWIR and LWIR wavelengths. The effective bandgap energies of InAs/InAs1-xSbx SLs with x = 0.28 - 0.40 are designed using a three-band envelope function approximation model. Multiple 0.5 μm-thick SL samples are grown by molecular beam epitaxy on GaSb substrates. Structural characterization using x-ray diffraction and atomic force microscopy reveals excellent crystalline properties with SL zero-order peak full-width-half-maximums between 30 and 40 arcsec and 20 x 20 μm2 area root-mean-square roughnesses of 1.6 - 2.7 A. Photoluminescence (PL) spectra of these samples cover 5 to 8 μm, and the band offset between InAs and InAs/InAs1-xSbx is obtained by fitting the PL peaks to the calculated values. The bowing in the valence band is found to depend on the initial InAs/InSb valence band offset and changes linearly with x as CEv_bowing = 1.58x - 0.62 eV when an InAs/InAs1-xSbx bandgap bowing parameter of 0.67 eV is assumed. A fractional valence band offset, Qv = ΔEv/ΔEg, of 1.75 ± 0.03 is determined and is practically constant in the composition range studied.

Mid-IR Interband Cascade Lasers

Efficient mid-IR interband cascade (IC) lasers have been developed based on III-V semiconductor materials with lasing emission covering a wavelength range from 2.7 to 5.6 microns. These IC lasers reuse injected electrons in cascade stages for photon generation with high quantum efficiency to achieve high output powers. Also, IC lasers have a low threshold current density with a very efficient use of applied voltage, resulting in reduced power consumption. Single-mode distributed feedback lasers have been made, and integrated into aircraft and balloon instruments which made atmospheric measurements of CH 4 and HCl. In this work, the characteristics of IC lasers and their recent developments are reviewed.

Recent progress in interband cascade lasers with separate confinement layers

Interband cascade lasers are efficient and compact semiconductor mid-infrared (3-6 μm) light sources with low-power consumptions. We report our recent progress in the development of interband cascade lasers with separate confinement layers. Broad-area (0.1mmx1mm) lasers have been operated in cw mode at temperatures up to 213K near 3.36 μm. For narrow ridge-waveguide (0.01mmx1.5mm) lasers, cw operation has been achieved at temperatures up to 266K near 3.43 μm, 260K near 3.7 μm, and 238K near 4.04 μm. The results on both broad-area and narrow-ridge IC lasers are discussed in comparison with previous regular IC lasers without separate confinement layers.

Mid-wave interband cascade infrared photodetectors based on GaInAsSb absorbers

In this work, we report the demonstration of quaternary GaInAsSb-based mid-wavelength infrared photodetectors with cutoff wavelengths longer than 4 μm at 300 K. Both interband cascade infrared photodetector (ICIP) with a three-stage discrete absorber architecture and conventional one-stage detector structures have been grown by molecular beam epitaxy and investigated in experiments for their electrical and optical properties. High absorption coefficient and gain were observed in both detector structures. The three-stage ICIPs had superior carrier transport over the one-stage detectors. A detectivity as high as 1.0 × 109 cm Hz1/2 W−1 was achieved at 3.3 μm for both one- and three-stage detectors under zero bias at 300 K. The implications of these results are discussed along with potential of GaInAsSb-based ICIPs for high-speed applications.