M. N. Kutty

Performance improvement of longwave infrared photodetector based on type-II InAs/GaSb superlattices using unipolar current blocking layers

We report here a heterojunction band gap engineered type-II InAs/GaSb strained layer superlattice photodiode for longwave infrared detection. The reported PbIbN architecture shows improved performance over conventional PIN design due to unipolar current blocking layers. At 77 K and Vb=−0.25 V, responsivity of 1.8 A/W, dark current density of 1.2 mA/cm2, single pass quantum efficiency of 23%, and shot noise limited detectivity (D∗) of 8.7×1010 cm Hz1/2 W−1 (λc=10.8 μm) were measured. The device demonstrated background limited performance at 100 K under 300 K for 2π field of view.

Varshni parameters for InAs/GaSb strained layer superlattice infrared photodetectors

The temperature-dependent behaviour of the bandgap of mid- and long-wavelength as well as dual-colour (mid-/long-wavelength) infrared detectors based on InAs/GaSb strained layer superlattices (SLSs) with p-i-n and nBn designs has been investigated with temperature-dependent absorption, photoluminescence and spectral response techniques. Values of Varshni parameters, zero temperature bandgap E0 and empirical coefficient α, were extracted and tabulated. The MWIR and LWIR superlattice detectors showed a temperature change of 0.325 meV K−1 and 0.282 meV K−1, respectively. These values are a factor of two lower than that of HgCdTe and InSb, making them attractive for higher operating temperatures.

GaSb quantum-well-based “buffer-free” vertical light emitting diode monolithically embedded within a GaAs cavity incorporating interfacial misfit arrays

The authors demonstrate a monolithic, electrically injected, vertically emitting GaSb∕AlGaSb light emitting diode (LED) emitting at 1.6μm comprised of a hybrid GaAs∕GaSb-based structure. The LED is comprised of a GaSb∕AlGaSb quantum well/barrier active region embedded within high index contrast GaAs∕AlGaAs distributed Bragg reflectors (DBRs) using two interfacial misfit (IMF) arrays to relieve the strain induced from the high 8% lattice mismatch between the material systems. The first IMF is formed under compressive strain conditions to enable strain-free, defect-free deposition of GaSb active region directly on the lower GaAs∕AlAs DBRs without need for thick buffer. The second IMF is formed under tensile conditions to enable the upper GaAs∕AlAs DBRs on the GaSb active region. The device demonstrates a maximum output power of 3.5μW. Initial diode optical and electrical characteristics along with IMF band structure are discussed.

Vertical minority carrier electron transport in p-type InAs/GaSb type-II superlattices

Vertical minority carrier electron transport parameters in p-type InAs/GaSb type-II superlattices for long wavelength infrared (LWIR) detection have been extracted from magnetic field dependent geometrical magneto-resistance. The measurements, performed at low electric fields and at magnetic field intensities up to 12 T, exhibited multiple-carrier conduction characteristics that required mobility spectrum analysis for the extraction of individual carrier mobilities and concentrations. Within the common operating temperature range for LWIR photodiodes (80 to 150 K), the conductivity was found to be dominated by three distinct carriers, attributed to majority holes (μ=280±27 cm2/Vs), minority electrons (μ=2,460±75 cm2/Vs), and parasitic sidewall inversion layer electrons (μ=930±55 cm2/Vs). A miniband energy gap of 140 ± 15 meV for the 14/7-monolayer InAs/GaSb superlattice was estimated from the thermal activation of the minority carrier electron density.

Room-temperature lasing at 1.82μm of GaInSb∕AlGaSb quantum wells grown on GaAs substrates using an interfacial misfit array

The authors report the device characteristics of GaInSb∕AlGaSb quantum well (QW) lasers monolithically grown on GaAs substrates. The 7.8% lattice mismatch between GaAs substrates and GaSb buffer layers can be completely accommodated by using an interfacial misfit (IMF) array. Room-temperature lasing operation is obtained from a 1.25-mm-long device containing six-layer Ga0.9In0.1Sb∕Al0.35Ga0.65Sb QWs at 1.816μm with a threshold current density of 1.265kA∕cm2. The observed characteristic temperature and temperature coefficient are 110K and 9.7A∕K, respectively. This IMF technique will enable a wide range of lasing wavelengths from near-infrared to midwavelength-infrared regimes on a GaAs platform.

Room-Temperature Operation of Buffer-Free GaSb–AlGaSb Quantum-Well Diode Lasers Grown on a GaAs Platform Emitting at 1.65

Buffer-free growth of GaSb on GaAs using interfacial misfit (IMF) layers may significantly improve the performance of antimonide-based emitters operating between 1.6 and 3 mum by integrating III-As and III-Sb materials. Using the IMF, we are able to demonstrate a GaSb-AlGaSb quantum-well laser grown on a GaAs substrate and emitting at 1.65 mum, the longest known operating wavelength for this type of device. The device operates in the pulsed mode at room temperature and shows 15-mW peak power at -10degC and shows high characteristic temperature (To) for an Sb-based active region. Further improvements to IMF formation can lead to high-performance lasers operating up to 3 mum.

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The authors report the InAs/InGaAs/GaAs/AlGaAs quantum dots-in-double-well (D-DWELL) design, which has a lower strain per DWELL stack than the InAs/InGaAs/GaAs DWELLs thereby enabling the growth of many more stacks in the detector. The purpose of this study is to examine the effects of varying the number of stacks in the double DWELL detector on its device performance. The structures are grown by solid source molecular beam epitaxy on GaAs substrates. After fabrication of single pixel devices, a series of device measurements such as spectral response, dark current, total current, and responsivity were undertaken and the photoconductive gain and the activation energies were extracted. The goal of these experiments is not only to optimize the device performance by optimizing the number of stacks but also to investigate the transport properties as a function of the number of stacks.

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We report the formation and growth characteristics of an interfacial misfit (IMF) array between AlSb and Si and its application to III-Sb-based quantum-well broad-area edge-emitting laser diodes monolithically grown on an Si (001) substrate. A 13% lattice mismatch between AlSb and Si is accommodated by using the IMF array. A use of 5deg miscut Si substrates enables simultaneous IMF formation and suppression of an antiphase domain, resulting in a drastic suppression of dislocation density over the III-Sb epilayer and realization of electrically injected laser diodes operating at 77 K. The current-voltage characteristics indicate a diode turn-on of 0.7 V, which is consistent with a theoretical built-in potential of the laser diode. This device is characterized by a 9.1-Omega forward resistance and a leakage current density of 0.7 A/cm2 at -5 V and 46.9 A/cm2 at -15 V.

Investigation of multistack InAs/InGaAs/GaAs self-assembled quantum dots-in-double-well structures for infrared detectors

We report the compensation of interfacial states formed by interfacial misfit dislocation (IMF) arrays via δ-doping. The IMF arrays are located inside the “buffer-free” heterojunction of GaSb/GaAs (001). The interfacial states are measured using surface photovoltage measurements and are positioned at 0.41, 0.49, and 0.61 eV. A higher reverse bias leakage current (IRB) was observed in the heterogeneous GaSb/GaAs IMF sample (73 μA at −5 V) compared to the homogeneous GaAs control sample (3.9 μA), which does not contain IMF. This increase in IRB is attributed to the interfacial states. Hence, the interfacial states are compensated by δ-doping the GaSb/GaAs interface using Te atoms. A low turn-on voltage of 0.85 V and a very low IRB of 0.1 nA were achieved for the δ-doped sample compared to the control and IMF samples. Hence, for optoelectronic applications, such as lasers, solar cells, and detectors, this compensated IMF technology is useful for integration of buffer-free III-Sb devices on an inexpensive GaA...

Monolithically Integrated III-Sb-Based Laser Diodes Grown on Miscut Si Substrates

The device fabrication and integration of nanopatterned quantum dots (PQDs) are realized through the demonstration of a broad-area light-emitting diode with PQD active region. The device involves two growth processes, first to form PQDs by selective-area epitaxy on an SiO(2) mask and then to complete the device structure after mask removal. Linear current-voltage characteristics are observed with sharp turn-on, low leakage current and low forward resistance. Electroluminescence spectra show PQD intraband structure and low quenching of emission from 77 K to room temperature. Light-current measurements demonstrate external quantum efficiency per PQD comparable to self-assembled QDs, thus providing a possible route toward individually addressable single QD devices.