AlSb Barrier Layers Research Articles

Bulk InAsxSb1-x nBn photodetectors with greater than 5μm cutoff on GaSb

Mid-wavelength infrared nBn photodetectors based on bulk InAsxSb1-x absorbers with a greater than 5 μm cutoff grown on GaSb substrates are demonstrated. The extended cutoff was achieved by increasing the lattice constant of the substrate from 6.09 to 6.13 Å using a 1.5 μm thick AlSb buffer layer to enable the growth of bulk InAs0.81Sb0.19 absorber material. Transitioning the lattice to 6.13 Å also enables the use of a simple binary AlSb layer as a unipolar barrier to block majority carrier electrons and reduce dark current noise. Individual test devices with 4 μm thick absorbers displayed 150 K dark current density, cutoff wavelength, and quantum efficiency of 3 × 10−5 A/cm2, 5.31 μm, and 44% at 3.4 μm, respectively. The instantaneous dark current activation energy at a given bias and temperature is determined via Arrhenius analysis from the Dark current vs. temperature and bias data, and a discussion of valence band alignment between the InAsxSb1-x absorber and AlSb barrier layers is presented.

Magneto-infrared modes in InAs-AlSb-GaSb coupled quantum wells

We have studied a series of InAs/GaSb coupled quantum wells using magneto-infrared spectroscopy for high magnetic fields up to 33 T within temperatures ranging from 4 to 45 K in both Faraday and tilted field geometries. This type of coupled quantum wells consists of an electron layer in the InAs quantum well and a hole layer in the GaSb quantum well, forming the so-called two-dimensional electron-hole bilayer system. Unlike the samples studied in the past, the hybridization of the electron and hole subbands in our samples is largely reduced by having narrower wells and an AlSb barrier layer interposed between the InAs and the GaSb quantum wells, rendering them weakly hybridized. Previous studies have revealed multiple absorption modes near the electron cyclotron resonance of the InAs layer in moderately and strongly hybridized samples while only a single absorption mode was observed in the weakly hybridized samples. We have observed a pair of absorption modes occurring only at magnetic fields higher than 14 T, which exhibited several interesting phenomena. Among which we found two unique types of behavior that distinguish this work from the ones reported in the literature. This pair of modes is very robust against rising thermal excitations and increasing magnetic fields aligned parallel to the heterostructures. While the previous results were aptly explained by the antilevel crossing due to the hybridization of the electron and hole wave functions, i.e., conduction-valence Landau-level mixing, the unique features reported in this paper cannot be explained within the same concept. The unusual properties found in this study and their connection to the known models for InAs/GaSb heterostructures will be discussed; in addition, several alternative ideas will be proposed in this paper and it appears that a spontaneous phase separation can account for most of the observed features.

Hole mobility in pseudomorphic InGaSb quantum well modulation doped with carbon

Carbon-tetrabromide (CBr4) is utilized as the p-type doping source in modulation-doped pseudomorphic In0.3Ga0.7Sb/AlxGa1−xSb quantum well structure. Carbon delta-doping is achieved by switching off group III elements while the flow of CBr4 is on during the growth of AlSb barrier layer. The hole mobility of strained In0.3Ga0.7Sb quantum well decreases monotonically from 600 to 400 cm2/V s while the sheet carrier concentration increases from 7.5×1011 to 4.1×1012 cm−2 with increasing carbon delta-doping.

InAlSb/InAs/AlGaSb Quantum Well Heterostructures for High-Electron-Mobility Transistors

Heterostructures for InAs-channel high-electron-mobility transistors (HEMTs) were investigated. Reactive AlSb buffer and barrier layers were replaced by more stable Al0.7Ga0.3Sb and In0.2Al0.8Sb alloys. The distance between the gate and the channel was reduced to 7–13 nm to allow good aspect ratios for very short gate lengths. In addition, n+-InAs caps were successfully deposited on the In0.2Al0.8Sb upper barrier allowing for low sheet resistance with relatively low sheet carrier density in the channel. These advances are expected to result in InAs-channel HEMTs with enhanced microwave performance and better reliability.

Large negative persistent photoconductivity in InAs∕AlSb quantum wells

Negative persistent photoconductivity in backgated InAs∕AlSb quantum wells under red and blue light emitting diode illumination is observed to depend on both illumination energy and intensity. During these experiments the electron sheet density is varied by one order of magnitude from 5.6×1011 to 5.8×1010cm−2. This behavior is attributed to the role of optically excited holes in the AlSb barrier layers near the InAs quantum well. Furthermore, a long relaxation time in the electron sheet density is observed and attributed to the slow movement of electrons from the InAs quantum well to ionized deep levels in the AlSb barriers.

Near-infrared intersubband transitions in delta-doped InAs∕AlSb multi-quantum wells

Intersubband transitions (ISBTs) in narrow InAs∕AlSb multiple quantum wells (MQWs) were investigated for well widths, d, ranging from 5 nm down to 1.8 nm with 10, 20, or 60 periods. In order to observe a strong ISBT signal, a heavy silicon doping was made in each InAs quantum well. Delta doping was employed for the narrowest wells to prevent silicon incorporation into the AlSb barrier layers. As the well width decreased, the ISBT signal of the MQWs decreased. However, it persisted down to d=2.1nm with a sheet doping density in each quantum well of 9×1012cm−2 and 60 periods. The ISBT signal observed for d=2.1nm was peaked at an energy of 650 and 670 meV at 300 and 77 K, respectively. These are the highest energy values ever observed for ISBTs in InAs∕AlSb MQWs.

A self-consistent investigation of the semimetal–semiconductor transition in InAs/GaSbquantum wells under external electric fields

We investigate the phase transitions in InAs/GaSb quantum wells sandwiched between twowide-gap AlSb barrier layers under an external electric field perpendicular to interfaces.The Schrödinger and the Poisson equations are solved self-consistently to derive the subbanddispersions, the potential profile, the electron charge distribution in the InAs layer,and the hole charge distribution in the GaSb layer. The Burt–Foreman envelopefunction theory and the scattering matrix method are used to solve the Schrödingerequation in the framework of the eight-band model, including the spin-splitting of subbands in our calculation. We have found that ina thick InAs/GaSb quantum well, which has been investigated experimentallyby Cooper et al (1998 Phys. Rev. B 57 11915), under low external electric fields,two electron levels stay below the highest hole level at zero in-plane wavevectork‖ = 0. Then, the anticrossings of electron and hole levels produce several minigaps in thein-plane dispersions, inside which the states of other subbands exist. As a result, thesystem is in a semimetal phase. With increasing external electric field, the semimetal phasechanges to semiconductor phase with only one hybridization gap. When all electronlevels become higher than the hole levels at higher electric fields, the system has asemiconducting gap.

Landau level structures and semimetal-semiconductor transition in strained InAs/GaSb quantum wells

Using Burt's envelope function theory and the scattering matrix method, we investigate the hybridized electron-hole Landau levels in strained InAs/GaSb quantum wells sandwiched between wide-gap AlSb barrier layers under electric and a quantizing magnetic fields applied perpendicular to interfaces. At zero magnetic field, in the structures studied here, the lowest electron level in the InAs layer lies below the highest heavy-hole level in the GaSb layer. With increasing magnetic field, the electron levels move up and the heavy-hole levels move down, producing anticrossings and gaps in the Landau level structures. We have found that the Landau level structures depend strongly on the lattice-mismatched strain and the applied voltage. As a result, in the region before anticrossings, the g factor of the lowest electron Landau level has a larger value for the quantum well structure grown on GaSb than that for the structure grown on InAs, while in the region after anticrossings the situation reverses for the g factor. Under low magnetic field, the difference between the electron g factors for the structures grown on different substrates is found to be as large as 10 for zero bias and decreases significantly with increasing bias. When all electron levels become higher than hole levels at high magnetic fields, the semimetal-semiconductor transition occurs. The critical magnetic field ${B}_{c}$ for the phase transition in structures grown on InAs is found to be lower than that in structures grown on GaSb. It is also obtained that a positive voltage biased across the InAs/GaSb well essentially decreases ${B}_{c}.$ Therefore, for a fixed magnetic field, the semimetal-semiconductor transition can be controlled by a bias.

Energy Relaxation Time and Microwave Noise in InAs/AlSb/GaSb/GaAs Heterostructures

Experimental technique based on microwave noise measurements is used to evaluate energy dissipation by hot electrons in a type II heterostructure consisting of InAs and GaSb with a thin AlSb barrier layer between them and containing a two-dimensional electron gas (2DEG). The energy relaxation time is estimated at 80 K and 300 K lattice temperatures. The energy relaxation time is almost independent of electric field and lattice temperature.

Room-temperature InAsSb strained-layer superlattice light-emitting diodes at λ=4.2 μm with AlSb barriers for improved carrier confinement

Room-temperature InAs/InAs1−xSbx strained-layer superlattice light-emitting diodes (x∼8%) are reported that emit at λ∼4.2 μm with an internal efficiency of 2.8%. The structures are grown by molecular beam epitaxy on slightly mismatched InAs substrates and include a strained AlSb barrier layer to prevent electron migration to the dislocated substrate–epilayer interface region. Comparison with a near identical structure grown without the barrier layer indicates a factor of four improvement in device efficiency at room temperature.

Resonant interband tunneling current in InAs/AlSb/GaSb/AlSb/InAs diodes with extremely thin AlSb barrier layers

We have investigated the resonant interband tunneling current in InAs/AlSb/GaSb/AlSb/InAs double-barrier resonant interband tunneling diodes with extremely thin AlSb barriers. Although no negative differential resistance (NDR) was observed for the diode without AlSb barrier layers, NDR appeared when 0.5-monolayer(ML)-thick AlSb barrier layers were inserted. As the thickness of AlSb barriers (Lb) increased from 0.5 to 2 ML, the difference between the peak current density and the valley current density increased. This result indicates the crucial role of the extremely thin AlSb barrier layers that are responsible for the resonance level and move it up toward the GaSb valence-band edge with an increase in Lb.

Growth and characterization of Sb-based heterostructures grown by LP-MOVPE

GaSbAlSb, InAsAlSb and InAsInP0.69Sb0.31 multi-quantum well structures were grown successfully by metalorganic vapor phase epitaxy. The good structural and optical quality was characterized by a combination of Raman spectroscopy and X-ray diffractometry. For the GaSbAlSb structures an unintentional incorporation of some percent Al in the GaSb well and of Ga in AlSb barrier layers was identified. At the interfaces of the material systems InAsAlSb and InAsInP0.69Sb0.31 our studies revealed the existence of InAsSb layers, which are explained in terms of the surfactant effect of Sb. The thickness and composition of these interlayers depend strongly on the InAs growth rate.

Large peak current densities in novel resonant interband tunneling heterostructures

We have observed negative differential resistance (NDR) and large peak current densities in a novel resonant interband tunneling structure grown by molecular beam epitaxy in the InAs/GaSb/AlSb material system. The structure consists of a thin AlSb barrier layer displaced from an InAs(n)/GaSp(p) interface. NDR is readily observable at room temperature with peak current densities greater than 105 A/cm2. The enhancement in peak current density relative to a structure with no AlSb barrier is consistent with the existence of a quasi-bound state in the region between the barrier and the InAs/GaAs interface. Furthermore, we demonstrate that by growing the AlSb layer on either the InAs or GaSb side of the interface, the quasi-bound state can be localized in either material.

InAs-AlSb heterostructure field-effect transistors fabricated using argon implantation for device isolation

We have fabricated planar heterostructure field-effect transistors with InAs quantum well channels and AlSb barrier layers. Argon implantation was used to form a damaged layer, which resulted in partial device to device isolation. A 1.5 μm gate device had a room-temperature extrinsic transconductance of 208 mS/mm.