Gain and internal losses in InGaAsSb/InAsSbP double-heterostructure lasers

We report on a study characterizing internal losses and the gain in InGaAsSb/InAsSbP diode-heterostructure lasers emitting in the mid-infrared (3–4 μm). Numerical simulations of the current dependence of the intensity of spontaneous emission above the laser threshold and of the differential quantum efficiency allowed us to determine the intraband absorption k ₀ ≈5.6×10⁻¹⁶ cm². The cavity-length dependence of the threshold current is used to estimate the internal losses at zero injection current α ₀≈5 cm⁻¹. Calculations of the internal losses at laser threshold showed that they increase more than fourfold when the cavity length is decreased from 500 μm to 100 μm. The temperature dependence of the differential quantum efficiency is explained on the assumption that intraband absorption with hole transitions into a split-off band occurs. It is shown that the maximum operating temperature of “short-cavity” lasers is determined by the intraband absorption rather than by Auger recombination. The internal losses are shown to have a linear current dependence. The separation of the quasi-Fermi levels as a function of current demonstrates an absence of voltage saturation of the p-n junction above threshold. Fiz. Tekh. Poluprovodn. 33, 759–763 (June 1999)     

InAsSb/InAsSbP double-heterostructure lasers emitting in the 3–4 µm spectral range

Our earlier reports concerning the fabrication by liquid-phase epitaxy and investigation of InAsSbP/InAsSb/InAsSbP double heterostructure lasers emitting at 3–4 μm are reviewed. The dependences of spectral characteristics and the spatial distribution of the laser emission on temperature and current are discussed. Lasing modes are shifted by 0.5–1.0 cm⁻¹ to longer wavelengths with increasing temperature. The tuning of the lasing modes by means of current is very fast (10⁻⁸–10⁻¹² s). With increasing current, the modes are shifted to shorter wavelengths by 50–60 ? at 77 K. The maximum mode shift of 104 ? (10 cm⁻¹) is observed at 62 K. The spectral line width of the laser is as narrow as 10 MHz. Abnormally narrow directional patterns in the p-n junction plane are observed in some cases in the spatial distribution of laser emission. The current tuning of lasers, due to nonlinear optical effects, has been modeled mathematically in good agreement with the experiment. Transmittance spectra of OCS, NH₃, H₂O, CH₃Cl, and N₂O gases were recorded using current-tuned lasers. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 12, 2001, pp. 1466–1480. Original Russian Text Copyright ? 2001 by Danilova, Imenkov, Kolchanova, Yakovlev. See [1].     

Energy spectrum of acceptors in the semimagnetic semiconductors p-Hg1−x MnxTe in the spin-glass region

The far-IR transmission and photoconductivity in the semimagnetic alloys p-Hg_1−x Mn_xTe (x=0.20–0.22) at temperatures 2–7 K were investigated at fixed frequencies of optically pumped molecular lasers in the region 49–311 μm. We report the observation of photoexcitation of acceptors from the ground into excited states under conditions when the direct interaction of the magnetic moments of the manganese ions becomes substantial and results in the formation of a spin-glass phase. It was found that the internal field produced by the spontaneous and external polarizations of the magnetic moments of the Mn²⁺ ions in the spin-glass temperature range influences the energy spectrum of acceptors in a magnetic field. Fiz. Tekh. Poluprovodn. 32, 450–452 (April 1998)     

Optical properties of crystals of the solid solutions (InSb)1−x (CdTe)x

The reflection and absorption spectra of crystals of the solid solutions (InSb)_1−x (CdTe)_x in the wavelength interval 2.5–25 μm were measured within the limits of solubility of CdTe in InSb (x⩽0.05) at room temperature. Analysis of the experimental results confirmed the applicability of the Kane theory for all compositions investigated. The variation of the optical band gap ɛ _g ^opt and the effective mass m _c at the Fermi level as a function of composition was determined. It is shown that the minimum values m _c=0.8×10⁻² m ₀ and ɛ _g ^opt =0.07 eV are reached for x=0.02–0.03. Information about the predominant mechanism of scattering for each alloy is obtained from the absorption curves in the region of absorption by free charge carriers. X-Ray crystallographic investigations were performed and the change Δa(x) in the lattice constant of the solid solutions relative to pure InSb was determined. It is shown that the behavior of m _c(x) and ɛ _g ^opt is uniquely determined by Δa(x). In turn, Δa(x) is determined by the complicated character of the interaction of the dopants with one another and with the InSb lattice. Fiz. Tekh. Poluprovodn. 32, 303–306 (March 1998)     

Photovoltaic effect in the impurity absorption region of Si-structures with blocked impurity conductivity

A study is made of the field dependence of the photoconductivity in two-layer Si:Sb-and Si:Bstructures with blocked impurity-band conductivity and different thicknesses of the undoped (blocking) layer. The impurity concentration in the doped (active) layer was ≈10¹⁸ cm⁻³. Measurements were made at temperatures T=4–15 K for high (Φ∼10¹⁶ photons/cm² · s) and low (Φ<10¹⁴ photons/cm² · s) incident photon fluxes. A photovoltaic effect is observed in the Si:B structures with a thin (3 μm) blocking layer. It is found that a photovoltage develops for photons with energies exceeding the ionization energy of boron and its magnitude is independent of the photoexcitation intensity (for Φ>10¹³ photons/cm² · s) and, in the limit of low temperatures, it is close to the activation energy ɛ ₃ for jump conductivity in the active layer. The photovoltaic effect is explained by ballistic transit of the blocking layer by holes emitted from the contact which are then cooled in the active layer, as well as by the presence of a potential barrier ≈ɛ ₃ between the active and blocking layers. These factors are taken into account in a model for describing the major features of the dependence of the photovoltage on temperature and on the photon intensity and energy. Fiz. Tekh. Poluprovodn. 33, 456–463 (April 1999)     

Staebler-Wronski effect as a function of the Fermi level position and structure of nondoped, amorphous, hydrated silicon

The photoconductivity degradation rates γ (σ _ph∼t ^−γ ) of nondoped, amorphous, hydrated silicon films deposited at T _s =300–400 °C and subjected to illumination for 5 h at 300 K (light source 100 mW/cm², λ<0.9 μm) were investigated. It was shown that the degradation rate γ depends on the preillumination position of the Fermi level ɛ _c −ɛ _F and often is not directly related to the hydrogen content in the film. It was found that there are correlations between the value of γ and the bonds in the silicon-hydrogen subsystem [isolated SiH and SiH₂ complexes, clusters (SiH)_n, and chains (SiH₂)_n]. Fiz. Tekh. Poluprovodn. 32, 484–489 (April 1998)     

Inversion of the conduction type of epitaxial films of PbSnTe solid solutions under the influence of laser irradiation at subthreshold power

Conduction type inversion processes in Pb_1−x Sn_xTe epitaxial films irradiated by a CO₂ laser (λ=10.6μm) at subthreshold power is investigated. It is hypothesized that the stable inverted state is a result of the formation of neutral metal and chalcogen divacancies. Fiz. Tekh. Poluprovodn. 31, 990–992 (August 1997)     

Effect of the charge state of defects on the light-induced kinetics of the photoconductivity of amorphous hydrated silicon

The photoconductivity and defect density in films of nondoped a-Si:H soaked with light (W=114 mW/cm², λ<0.9 μm) for 5 h were investigated. It is shown that σ_ph ~ t ^-γ and N _D ~ t ^β, where γ>β or γ⋍β, depending on the position of the Fermi level prior to light soaking, i.e., depending on the charge state of the defects: D ⁻ and D ⁰ or D ⁺ and D ⁰. It is also shown that the light-induced kinetics of σ _ph is affected by a transition of the defects into the D ⁰ state because of a corresponding shift of the Fermi level during light soaking. Fiz. Tekh. Poluprovodn. 32, 345–348 (March 1998)     

Effect of successive implantation of Ag+(Cu+) and Xe+ ions on the recombination properties of CdxHg1−x Te crystals

The effect of successive double implantation of Ag⁺(Cu⁺) and Xe⁺ ions on the recombination properties of Cd_xHg_1−x Te (0.2<x<0.3) crystals has been investigated. It is shown that after implantation of ions of one chemical element, followed by diffusion thermal annealing at temperatures below 150–200 K, recombination through local levels lying 30±5 meV below the conduction band bottom dominates. Successive double implantation of Ag⁺(Cu⁺) and Xe⁺ ions followed by diffusion thermal annealing changes the course of the temperature dependence of the lifetime of the nonequilibrium charge carriers. It was determined that for Cd_xHg_1−x Te crystals with x⋍0.20–0.25 in the temperature interval 700–200 K the lifetime of the nonequilibrium charge carriers is low (τ<0.15 μs) and does not depend on the temperature. For Cd_xHg_1−x Te crystals with x⋍0.3 recombination of nonequilibrium charge carriers occurs through two types of levels: in the temperature range 140–200 K — deep levels E _t1⋍E _c −51 meV and at lower temperatures (77–140 K) — through shallower levels E _t2⋍E _c −(16±2) meV. Fiz. Tekh. Poluprovodn. 31, 786–789 (July 1997)     

Interband absorption of long-wavelength radiation in δ-doped superlattices based on single-crystal wide-gap semiconductors

A new type of superlattice formed in a single-crystal nondegenerate, wide-gap semiconductor by a sequence of pairs of closely spaced, δ-doped donor and acceptor layers is proposed. It is shown that because of the superstrong electric fields generated between these δ-doped layers, the electroabsorption of long-wavelength radiation is determined by tunneling optical transitions of electrons from the heavy-hole band (in contrast to the case of moderately strong fields when the electroabsorption is determined by light holes). The magnitude of the electroabsorption is close to the interband absorption for light and is virtually independent of the photon energy up to the far-infrared region. It was found that in the proposed InSb-based superlattice the absorption in superstrong fields can exceed 10³ cm⁻¹ up to radiation wavelengths approximately equal to 50–100 μm. It is noted that because of the spatial separation of the photogenerated electrons and holes, their lifetime and the long-wavelength sensitivity of such a superlattice have giant values. Fiz. Tekh. Poluprovodn. 32, 221–226 (February 1998)     

Mobility of charge carriers in double-layer PbTe/PbS structures

The method of hot-wall epitaxy is used to grow epitaxial heterostructures of p-PbTe/n-PbS on BaF₂ substrates. Hall-effect measurements are analyzed in order to obtain the dependence of the effective carrier mobility on thickness and temperature in the ranges 0.1–2 μm and 100–300 K, respectively. It is found that this mobility depends on the thickness of the sample and on the individual thicknesses of its constituent layers. The effective mobility is calculated under the assumption that charge carriers are scattered by the surface of the structure and by dislocations that form at the heterojunction boundary. Fiz. Tekh. Poluprovodn. 32, 1064–1068 (September 1998)     

Use of two low-temperature emitters to determine the cutoff wavelength of the photosensitivity of infrared photodetectors

This paper is the continuation of the analysis of a method of determining the cutoff wavelength λ _c of infrared photodetectors by irradiating the sample with radiation from two blackbodies with different temperatures. The emitters can operate at lower temperatures as the cutoff wavelength λ _c is increased. The parameters of a system employing two blackbodies, which are placed inside a liquid-nitrogen cryostat and have temperatures of 260 and 320 K, respectively, are presented. It is shown that an error of 1 K in determining the lower or higher temperature produces an error of approximately 0.3 and 0.2 μm, respectively, in λ _c if λ _c=10 μm. Measurements on photodiodes fabricated on the basis of Cd_0.24Hg_0.76Te (λ _c=8.1 μm) epitaxial layers showed that the difference in the values of λ _c obtained by this method and from spectral measurements is no more than several tenths of a micron. It is suggested that this method be used as a standard method. Fiz. Tekh. Poluprovodn. 32, 1135–1138 (September 1998)     

Photosensitivity of In-SiO2-Cd0.28Hg0.72Te structures with a nontransparent field electrode

The photoeffect in a metal-insulator-semiconductor (MIS) structure that incorporated a Cd_0.28Hg_0.72Te compound, a low-temperature pyrolitic SiO₂, and an In layer with a thickness of 500 nm and an area of 0.5×0.5 mm² was studied. For a MIS structure with a nontransparent field electrode, the observed photoeffect consists in variation in the capacitance and high-frequency electrical conductivity of the MIS structure; this photoeffect is caused by photocarriers that are formed outside the MIS structure and reach this structure either due to diffusion or along the surface channel. This happens if the MIS structure is in the state of inversion; in this case, an eddy electric current formed crosses the induced p-n junction and closes on itself at the MIS structure periphery. It is assumed that this current and the extra voltage across the p-n junction are related by the Shockley formula. The following parameters were evaluated: the coefficient β in the Shockley formula (β characterizes the nonideality of the p-n junction); the product R ₀ A of the resistance for zero bias by the area of the p-n junction; and the surface area ΔS of collection of the charge carriers. It was found that β=1.52, R ₀ A=2.7×10⁵ Ω cm², and ΔS corresponds to a stripe that goes along the MIS-structure perimeter and has a width of 15 μm. The MIS structure studied is considered as a photodetector. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 7, 2000, pp. 822–826. Original Russian Text Copyright ? 2000 by Ovsyuk, Vasil’ev, Mashukov.     

Photoelectrical memory in GaAs/AlGaAs multilayer quantum-well structures

An increase in the dark current (by 2–3 orders of magnitude) in GaAs/Al_xGa_1−x As multilayer quantum-well structures with x⋍0.4 is observed after illumination of the structures with optical light (λ<1.3 μm). This increase is sustained for an extended time (more than 10³ s) at low temperatures. It then decreases to its initial value upon heating of the sample. A model of the barrier with local sag of the conduction band facilitating tunneling is proposed. The conduction band sag and the magnitude of the current grow due to optical ionization of uncontrolled deep level clusters present in the barrier and decrease due to subsequent capture of electrons from the conduction band by the deep levels upon heating. Fiz. Tekh. Poluprovodn. 32, 209–214 (February 1998)     

Ultralow internal optical loss in separate-confinement quantum-well laser heterostructures

Internal optical loss in separate-confinement laser heterostructures with an ultrawide (>1 smm) waveguide has been studied theoretically and experimentally. It is found that an asymmetric position of the active region in an ultrawide waveguide reduces the optical confinement factor for higher-order modes and raises the threshold electron density for these modes by 10–20%. It is shown that broadening the waveguide to above 1 μm results in a reduction of the internal optical loss only in asymmetric separate-confinement laser heterostructures. The calculated internal optical loss reaches ∼0.2 cm⁻¹ (for λ≈1.08 μm) in an asymmetric waveguide 4 μm thick. The minimum internal optical loss has a fundamental limitation, which is determined by the loss from scattering on free carriers at the transparency carrier density in the active region. An internal optical loss of 0.34 cm⁻¹ was attained in asymmetric separate-confinement laser heterostructures with an ultrawide (1.7 μm) waveguide, produced by MOCVD. Lasing in the fundamental transverse mode has been obtained owing to the significant difference in the threshold densities for the fundamental mode and higher-order modes. The record-breaking CW output optical power of 16 W and wallplug efficiency of 72% is obtained in 100-μm aperture lasers with a Fabry-Perot cavity length of ∼3 mm on the basis of the heterostructures produced. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 12, 2004, pp. 1477–1486. Original Russian Text Copyright ? 2004 by Slipchenko, Vinokurov, Pikhtin, Sokolova, Stankevich, Tarasov, Alferov.     

Pulsed-magnetron-sputtered low-temperature indium tin oxide films for flat-panel display applications

In this paper, indium tin oxide (ITO) thin films were prepared by unipolar and bipolar direct current (DC)-pulsed magnetron sputtering in a mixture of argon and oxygen onto unheated glass substrates. The target of ITO with 10 wt.% tin is used. The influences of polar modes (unipolar and bipolar); output frequencies (0 to 33 kHz); and times and off times on the optical, electrical, and structural properties of ITO films are investigated. The correlations between the deposition parameters and the film properties are discussed. It is found that the resistivity with 10⁻³ Θ-cm and transmittance with ≥90% of amorphous ITO films can be prepared by the reactive bipolar DC-pulsed sputtering with t _on ⁻ between 45 μs and 85 μs (i.e., t _on ⁻ /t _on ⁺ is 9–17), and t _on ⁺ , t _off ⁻ and t _off ⁺ are constant at 5 μs, 10 μs, and 5 μs, respectively. An optimal condition, based on the polar mode and frequency of reactive-pulsed sputtering, for obtaining the high transmittance and low resistivity of ITO films is suggested.     

<Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> photoreflectance spectra of semiconductor structures with a high density of interface states

The results of a photoreflectance spectroscopy study of Ga₂Se₃/n-GaAs samples prepared by long-term annealing of GaAs wafers (n≈10¹⁷ cm⁻³) in a Se-vapor atmosphere are presented. It was established that no photovoltage appears in the interface region of these structures under illumination. Photogeneration of the charge carriers in the substrate does not lead to a change in the Fermi level position at the interface, with only the depth of the space-charge region being modulated. The quantitative analysis of the spectra also indicates that the growth of a thick (∼ 1 μm) Ga₂Se₃ layer does not result in the expected shift of the Fermi level position in comparison to the natural oxide-covered surface. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 7, 2002, pp. 838–842. Original Russian Text Copyright ? 2002 by Kuz’menko, Domashevskaya.     

Manifestation of percolation conductivity of short-channel field-effect transistors in the spectrum of shallow interface states

The effective density of shallow interface states N _ss is investigated in the temperature range T=77–300 K using the field-effect method in short-channel (0.5–5 μm) Si-MNOS and GaAs-based FET’s with high (greater than 10¹² cm⁻²) concentrations of built-in charge in the subgate insulator. A peculiarity of the density of electronic states N _ss was found having the form of a peak, which manifests itself more distinctly at lower temperatures, higher concentrations of built-in charge, and shorter gates. The peak was observed at the same values of the channel conductance G∼q ²/h, regardless of variations in the above-enumerated parameters, the thickness of the sub-gate insulator, and the channel-length-to-width ratio. This means that the energy depth of the peak (∼40–120 meV) varies in proportion to T, which contradicts the current understanding of the interface states caused by both the fluctuation potential (FP) and surface defects or traps. The results are interpreted within the framework of percolation theory applied to the conductivity of strongly disordered systems. The N _ss peculiarity is associated with a transition from the conductivity of a two-dimensional effective solid, which occurs when the fluctuation potential is strongly screened by surface electrons, to conductivity via a quasi-one-dimensional potential trough organized by local regions with reduced surface potential under conditions of a strong fluctuation potential. Fiz. Tekh. Poluprovodn. 31, 1460–1467 (December 1997)     

Recombination mechanisms in doped n-type Hg1−x CdxTe crystals and properties of diffusion p +-n junctions based on them

We made p ⁺-n-type photodiodes for the 3–5 and 8–12 μm wavelength regions by diffusing As into single-crystal n-Hg_1−x Cd_xTe substrates, and investigated their electrical and photoelectric properties. Analysis of the temperature dependences of the differential resistance and current-voltage characteristics led us to conclude that charge-carrier transport is predominately due to the generation-recombination mechanism at a temperature of 77 K. As the temperature increases, a contribution from the diffusion component also appears. We obtained values of the product R ₀ A≅0.3–1.0, 1–10, and (1–10)×10⁴ Ω · cm² for diodes with long-wavelength photosensitivity cutoffs λ_c≅11.5, 10.5, and 6.0 μm, respectively, indicating that they could operate in the regime where performance is limited by background radiation fluctuations. Fiz. Tekh. Poluprovodn. 31, 350–354 (March 1997)     

Photoconductivity of sulfur-doped silicon near 10.6 µm

The extrinsic photoconductivity of Si〈S〉 under short-wavelength (10.6 μm) illumination was investigated in the pulsed regime. It was found that sensitivity can be increased by 2–3 orders of magnitude by short-wavelength illumination. It was established that increasing the degree of compensation of the impurity levels of sulfur by γ-ray-induced acceptors decreases both the dark conductivity and the photoresponse due to pulsed illumination with a CO₂ laser. Fiz. Tekh. Poluprovodn. 31, 1425–1427 (December 1997)