The electroluminescent properties of narrow-gap type II InAs/InSb/InAs heterostructures containing a single layer of InSb quantum dots placed at the interface of the p-n junction in InAs were studied. The features of the electroluminescence spectra depending on the surface density of nanoobjects at a broken-gap type II heterointerface were investigated both at forward and reverse bias. When applying a reverse bias to the heterostructures under study, the suppression of negative interband luminescence and the dominance of interface recombination transitions at the InSb/InAs type II heterojunction were observed at room temperature. The radiation, which corresponded to recombination transitions involving localized states of InSb quantum dots, was recorded at low temperature.

The results of theoretical and experimental studies of impact ionization processes and charge carrier heating in multi-valley A3B5 semiconductors at high electric field are presented and their relationship with the features of the band structure is discussed. A role of subsidiary L- and X-valleys, complex structure of the valence band and orientation dependence of the ionization coefficients are taken into account. A new approach to the choice of semiconductor materials with a large ratio of the ionization coefficients of holes and electrons to create the noiseless avalanche photodiodes due to monopolarity of hot charge carrier multiplication is proposed.

Asymmetrical double InAs/InAsSb/InAsSbP heterostructures are grown by metalorganic vapor-phase epitaxy. Two types of light–emitting diodes (A and B) were created on basis of grown heterostructures with emission peak at 4.1 µm and 4.7 µm, respectively. The current–voltage and electroluminescent characteristics of light–emitting diodes are investigated at room temperature. When operating at 50 % duty cycle mode (frequency − 512 Hz) with a current of 250 mA, light–emitting diodes A and B produced the optical power of 24 μW and 15 μW, respectively. Under the pulse operation (frequency − 512 Hz, duration − 1 μs) with a current of 2.1 A, the optical power of light–emitting diodes А and B reached the values of 158 μW and 76 μW, respectively. The developed light–emitting diodes can be used as high-effective radiation sources in optical absorption sensors for detection of carbon dioxide and carbon monoxide in the atmosphere.

AbstractThe electroluminescent characteristics of a type-II n -GaSb/ n -InAs/ p -GaSb heterostructure with a single deep quantum well grown by metalorganic vapor-phase epitaxy are investigated. The energy-band diagram of the structure and the positions of the electron and heavy-hole energy levels are calculated. The analysis of the current–voltage characteristics demonstrates that the dark current in the structure under study flows via the tunneling mechanism. Intense electroluminescence characterized by a weak temperature dependence was observed in the spectral range of 3–4 μm at T = 77 and 300 K. The main electroluminescence band ( h ν = 0.40 eV at 77 K) corresponds to direct radiative transitions between electrons from level E _1 in the InAs quantum well and heavy holes from the continuum at the n -GaSb/ n -InAs heterointerface. A low-intensity electroluminescence band at h ν = 0.27 eV ( T = 77 K) originates from indirect (tunneling) transitions from the first electron level in the quantum well to the second level of heavy holes localized in the valence-band “notch” at the n -InAs/ p -GaSb heterointerface.

AbstractAsymmetric n -InAs/InAs_(1 – _ y )Sb_ y / p -InAsSbP heterostructures with a narrow-gap active layer and a composition range y = 0.09–0.16 were grown by vapor phase epitaxy from metalorganic compounds. Room-temperature electroluminescence was observed at a wavelength of up to λ = 5.1 μm at a spectral maximum. The study of low-temperature electroluminescence spectra provided the possibility to establish the existence of two radiative recombination channels caused by the nature of the InAsSb/InAsSbP heterointerface. The effect produced by the chemistry of the active layer on the composition of the grown barrier layer and the formation of the InAsSb/InAsSbP heterojunction with an increase in the antimony content in the InAsSb solid solution was demonstrated.

We report on the unusually large blue shift of the electroluminescence spectrum with an increase of the drive current at 77 K in a doublebarrier nanoheterostructure with a deep AlSb/InAs0.83Sb0.17/AlSb quantum well grown by metal-organic vapor phase epitaxy on the n-GaSb:Te substrate. The rise of the drive current from 20mA to 220 mA led to a shift of the electroluminescence spectrum maximum toward higher photon energies by 100 meV. It was shown that this effect is due to indirect (tunneling) radiative transitions between electrons in InAsSb quantum well and heavy holes localized near the AlSb/p-GaSb heterointerface. The energy of radiative transition was linearly dependent on the applied voltage. In the drive current range of 50-220 mA, an electroluminescence blue shift was accompanied by spectrum narrowing by 40 meV and a noticeable change of the spectrum shape. With a rise in the drive current, a superlinear increase of the electroluminescence intensity caused by the nonlinear dependence of tunneling radiative recombination rate on transition energy was observed at 300 K and 77 K. Published under license by AIP Publishing.

AbstractSingle heterostructures of type II n ^+-InA s/n ^0-InAs_0.59Sb_0.16P_0.25, based on an intentionally undoped epitaxial layer with an electronic type of conductivity are obtained by metalorganic vapor phase epitaxy (MOVPE). In the heterostructure, a transition layer of modulated composition is formed near the heterointerface in the bulk of the quaternary solid solution. The existence of a radiative recombination channel due to the presence of localized hole states in quantum wells formed in the transition layer near the heterointerface is shown. It is demonstrated that the maximum of the intensity of the electroluminescence spectrum of the heterostructure under study is rearranged when a forward external bias is applied. The results of this study can be used in the development of tunable light-emitting diodes operating in the midinfrared range of 2–4 μm.

AbstractSignificant photocurrent/photoconductivity amplification is observed at low reverse biases in a type-II n -GaSb/InAs/ p -GaSb heterostructure with a single quantum well (QW), grown by metal-organic vapor phase epitaxy. A sharp increase in the photocurrent by more than two orders of magnitude occurs under exposure of the heterostructure to monochromatic light with a wavelength of 1.2–1.6 μm (at 77 K) and the application of a reverse bias in the range 5–200 mV. The optical gain depends on the applied voltage and increases to 2.5 × 10^2 at a reverse bias of 800 mV. Theoretical analysis demonstrated that the main role in the phenomenon is played by the screening of the external electric field by electrons accumulated in the deep InAs QW and by the mechanism of the tunneling transport of carriers with a small effective mass. It is shown that the effect under study is common to both isotype and anisotype type-II heterojunctions, including structures with QWs and superlattices.

We will report about the first observation of superlinear electroluminescence (EL) and enhancement of optical power in nano-heterostructures based on GaSb with a deep, narrow Al(As)Sb/InAsSb/Al(As)Sb quantum well (QW) in the active region, grown by metal organic vapor phase epitaxy. Structures were grown on n-GaSb:Te substrate with 20 nm Al(As)Sb/5 nm InAs0.84Sb0.16/20 nm Al(As)Sb QW and 0.5 μm p-GaSb cap layer, details of technology see in [1]. Emission coming from the structure through p-GaSb cap layer was measured. EL spectra were obtained for different currents and at temperatures 77 and 300 K. Dependences of EL spectra in the range 0.6-0.8 eV on the drive current (in the range 0-200 mA) are shown in the Fig. 1 for T = 300 and 77 K. Superlinear EL power dependence on driving current was found at both temperatures. Experimental optical power vs. current can be described by the power law P=AI, where A is a fitting parameter and index B varied for different samples in the range 2-3 at 300 K and 1.5-2 at 77 K (Fig. 2). These values are 1.5 times higher than for GaSb based heterostructures which were studied earlier [2]. These effects can be explained by electron impact ionization in Al(As)Sb/InAsSb QW in which a large conduction band offset at the interface ∆EC = 1.27 eV exceeds ionization threshold energy for electrons in the narrow-gap well, and by contribution of additional e-h pairs in radiative recombination. Theoretical calculation of the size quantization energy levels in QW is presented [3], and possible cases of impact ionization, depending on the band-offset at the interface and on the quantum well width, will be considered. A great interest is attracted to enhancement of quantum efficiency of photovoltaic cells based on QD nanostructures by using effect of multiplication under illumination by high-energy photon [4]. Capasso et al demonstrated a possibility to rise the electron ionization coefficient compared with the hole’s one by use of the large conduction band offset at GaAs/AlGaAs interface in superlattice avalanche photodiodes [5]. But this approach was not considered for QW lightemitting structures. These results can be also applied to improving parameters of solar and thermophotovoltaic cells. ACKNOWLEDGEMENT We acknowledge the useful comments by T. Šimeček. The work was supported by CSF Project P102/10/1201 and by the Institute of Physics scientific program AV0Z 10100521, by grant of RBRF RAS #12-02-00597 and grant of Presidium RAS Program #24. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0.50 0.55 0.60 0.65 0.70 0.75 Photon Energy (eV) E L In te ns ity (a .u .) 50 75 100 125 150 175 200

We report on the observation of superlinear electroluminescence (EL) in nanoheterostructures based on GaSb with a deep narrow Al(As)Sb/InAsSb/Al(As)Sb quantum well (QW) in the active region, grown by metal organic vapor phase epitaxy. Electroluminescence spectra for different driving currents were measured at temperatures of 77 and 300 K. It is shown that such structure exhibits superlinear dependence of optical power on the drive current and its increase of 2–3 times in the current range 50–200 mA. This occurs due to impact ionization in the Al(As)Sb/InAsSb quantum well in which a large band offset at the interface ΔEC = 1.27 eV exceeds ionization threshold energy for electrons in the narrow-gap well. Calculation of the size quantization energy levels is presented, and possible cases of impact ionization, depending on the band offset ΔEC at the interface and on the quantum well width, are considered. This effect can be used to increase quantum efficiency and optical power of light emitting devices (lasers), as well as for photovoltaic elements.

Intense mid-infrared (λ∼2μm) room temperature electroluminescence from metal organic vapor phase epitaxy (MOVPE) grown type-I single AlSb∕InAsSb∕AlSb quantum wells (QWs) is reported. The spectral position of the electroluminescent peaks is in good agreement with k∙p envelope function calculation in the frame of four-band Kane’s model taking into account the intermixing of s and p states in the deep quantum well. A four times increase of the emission intensity with temperature increasing from 77to300K can be explained by highly efficient radiative recombination of the electrons injected into the narrow AlSb∕InAsSb∕AlSb QW due to its specific design, leading to Auger process suppression.

A hybrid double heterostructure with large asymmetric band offsets, combining AlAsSb/InAs (as a III-V part) and CdMgSe/CdSe (as a II-VI part), has been proposed as a basic element of a mid-infrared laser structure design. The p-i-n diode structure has been successfully grown by molecular beam epitaxy (MBE) and exhibited an intense long-wavelength electroluminescence at 3.12•gm (300K). A 1I-VI MBE growth initiation with a thin ZnTe buffer layer prior to the CdMgSe deposition results in a dramatic reduction of defect density originating at the II-VI/III-V interface, as demonstrated by transmission electron microscopy. A less than 10 times reduction of electroluminescence intensity from 77 to 300K indicates an efficient carrier confinement in the InAs active layer due to high potential barriers in conduction and valence bands, estimated as AEc = 1.28 eV and AEv 1.6 eV. An increase in the pumping current results in a super-finear raising the EL intensity. The type of band line up at the coherent InAs/CdirMg.,Se interface is discussed for 0<x_0.2, using experimental data and theoretical estimations within a model-solid theory.