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)     

High-power light-emitting diodes operating in the 1.9 to 2.1-µm spectral range

Light-emitting diodes (LED’s) operating in the spectral range 1.9–2.1 μm have been fabricated by liquid-phase epitaxy on the basis of AlGaAsSb/GaInAsSb double heterostructures with a high Al (64%) content in the wide-gap regions. The design of the LED makes it possible to locate the active region near the heat-removal elements of the housing, and pass the light through the GaSb substrate, which is completely unshielded by the contact. The LED’s are investigated in the quasi-continuous (CW) regime and pulsed regime at room temperature. The optical power of the LED’s possesses a linear current dependence over a wide range of currents. A CW optical power as high as 4.6 mW and a peak optical power of 190 mW in the pulsed regime were achieved at room temperature. It is shown that the transition from linear to sublinear current dependence of the optical power is governed by Auger recombination in the pulsed regime at pulse durations as low as 5 μs. Fiz. Tekh. Poluprovodn. 33, 239–242 (February 1999)     

InAsSb/InAsSbP double-heterostructure lasers emitting at 3–4 µm: Part I

Previous publications concerned with the development and investigation of InAsSb/InAsSbP double heterostructure lasers emitting at 3–4 μm fabricated by liquid phase epitaxy are reviewed. In pulsed mode, the maximum operating temperature of the lasers is 203 K, the characteristic temperature is 35 K, and differential quantum efficiency is 20±5% at 77K. Mesa-stripe lasers with a 10-to 30-μm stripe width and a 200-to 500-μm cavity length can operate in CW mode up to 110 K. The total optical output power of more than 10 mW at λ=3.6 μm is obtained at T=82 K in CW mode. The output power per mode does not exceed 2 mW/facet. A single-mode lasing is achieved in the temperature range of 12–90 K. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 11, 2000, pp. 1396–1403. Original Russian Text Copyright ? 2000 by Danilova, Imenkov, Sherstnev, Yakovlev.     

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)     

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)     

Pulsed laser deposition and processing of wide band gap semiconductors and related materials

The present work describes the novel, relatively simple, and efficient technique of pulsed laser deposition for rapid prototyping of thin films and multi-layer heterostructures of wide band gap semiconductors and related materials. In this method, a KrF pulsed excimer laser is used for ablation of polycrystalline, stoichiometric targets of wide band gap materials. Upon laser absorption by the target surface, a strong plasm a plume is produced which then condenses onto the substrate, kept at a suitable distance from the target surface. We have optimized the processing parameters such as laser fluence, substrate temperature, background gas pressure, target to substrate distance, and pulse repetition rate for the growth of high quality crstalline thin films and heterostructures. The films have been characterized by x-ray diffraction, Rutherford backscattering and ion channeling spectrometry, high resolution transmission electron microscopy, atomic force microscopy, ultraviolet (UV)-visible spectroscopy, cathodoluminescence, and electrical transport measurements. We show that high quality AlN and GaN thin films can be grown by pulsed laser deposition at relatively lower substrate temperatures (750–800°C) than those employed in metal organic chemical vapor deposition (MOCVD), (1000–1100°C), an alternative growth method. The pulsed laser deposited GaN films (∼0.5 μm thick), grown on AlN buffered sapphire (0001), shows an x-ray diffraction rocking curve full width at half maximum (FWHM) of 5–7 arc-min. The ion channeling minimum yield in the surface region for AlN and GaN is ∼3%, indicating a high degree of crystallinity. The optical band gap for AlN and GaN is found to be 6.2 and 3.4 eV, respectively. These epitaxial films are shiny, and the surface root mean square roughness is ∼5–15 nm. The electrical resistivity of the GaN films is in the range of 10⁻²–10² Θ-cm with a mobility in excess of 80 cm²V⁻¹s⁻¹ and a carrier concentration of 10¹⁷–10¹⁹ cm⁻³, depending upon the buffer layers and growth conditions. We have also demonstrated the application of the pulsed laser deposition technique for integration of technologically important materials with the III–V nitrides. The examples include pulsed laser deposition of ZnO/GaN heterostructures for UV-blue lasers and epitaxial growth of TiN on GaN and SiC for low resistance ohmic contact metallization. Employing the pulsed laser, we also demonstrate a dry etching process for GaN and AlN films.     

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)     

Midwave-infrared negative luminescence properties of HgCdTe devices on silicon substrates

We have investigated the negative luminescence properties of a midwave-infrared (MWIR) HgCdTe photodiode (λ_co = 5.3 μm at 295 K) grown on a silicon substrate. The internal negative luminescence efficiencies measured using a self-referencing optical technique were 88% throughout the 3–5 μm spectral region and nearly independent of temperature in the 240–300 K range. This corresponds to an apparent temperature reduction of 53 K at room temperature and 35 K at 240 K. Efficiencies measured by an electrical modulation technique were consistent with the measured internal efficiencies and the measured reflectivity of the device. This is the highest efficiency and largest apparent reduction in temperature reported to date, and slightly higher than that measured earlier for photodiodes grown on CdZnTe despite a longer cut-off wavelength. These results provide further indication that the HgCdTe/Si photovoltaic device technology is capable of combining high quality with high yield.     

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].     

Nature of the edge electroluminescence peak in the Si:(Er,O) diode breakdown mode

Electroluminescence (EL) of erbium-and oxygen-doped Si:(Er,O) diodes at λ=1.00–1.65 μm has been studied in the p-n junction breakdown and forward current modes. The EL was measured at room temperature from the front and back surfaces of the diodes. A peak corresponding to the absorption band edge of silicon was observed in the EL spectra of some diodes in the p-n junction breakdown mode. The peak is associated with the injection of minority carriers from the metal contact into silicon, with subsequent band-to-band radiative recombination. The band-to-band recombination intensity increases sharply on reaching a certain current density that depends on the fabrication technology. This threshold current density decreases with the temperature of post-implantation annealing of Si:(Er,O) diodes increasing in the range 900–1100°C. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 4, 2002, pp. 453–456. Original Russian Text Copyright ? 2002 by Emel’yanov, Nikolaev, Sobolev.     

Influence of temperature on Auger recombination lifetime in In1?xGaxAs materials

The influence of temperature and Ga composition on Auger recombination lifetime in n-type and p-type In1-xGaxAs materials is investigated through the simulation, assuming the concentrations of electrons and holes are 1017 cm-3 and 1018 cm-3, respectively. The results show that the temperature has little influence on Auger recombination lifetime of In1-xGaxAs materials at x<0.3. However, it has a great impact when x>0.3 and the effect is more obvious at a lower temperature. Moreover, Auger ...     

Influence of growth conditions on the formation and luminescence properties of InGaAs quantum dots in a Si matrix

The influence of the growth conditions during molecular-beam epitaxy and of the degree of lattice mismatch between the epilayer and the substrate on the formation of InGaAs islands on a Si(100) surface is studied. An increase in lattice mismatch (the InAs mole fraction) leads to an increase in the critical thickness corresponding to the onset of island growth, in contrast to the formation of InGaAs islands on GaAs(100). An increase in the deposition temperature also increases the critical thickness, whereas an increase in the arsenic pressure has the opposite effect. Structures containing an array of InGaAs islands in a Si matrix display a luminescence line in the range 1.2–1.3 μm, depending on the mole fraction of InAs. Fiz. Tekh. Poluprovodn. 33, 194–197 (February 1999)     

Long-wavelength emission in structures with quantum dots formed in the stimulated decomposition of a solid solution at strained islands

When an array of strained InAs nanoislands formed on a GaAs surface is overgrown by a thin (1–10 nm) layer of an indium-containing solid solution, stimulated decomposition of the solid solution is observed. This process causes the formation of zones of elevated indium concentration in the vicinity of the nanoislands. The volume of newly formed InAs quantum dots increases as a result of this phenomenon, producing a substantial long-wavelength shift of the photoluminescence line. This effect is enhanced by lowering the substrate temperature, and it depends weakly on the average width of the band gap of the solid solution. The indicated approach has been used successfully in achieving room-temperature emission at a wavelength of 1.3 μm. Fiz. Tekh. Poluprovodn. 33, 990–995 (August 1999)     

Current-voltage characteristics of Si:B blocked impurity-band structures under conditions of hopping-transport-limited photoresponse

The photoconductivity of Si:B blocked-impurity-band (BIB) structures with boron concentration in the active layer ∼10¹⁸ cm⁻³ has been studied. Measurements were performed in the temperature range 4.2–10 K at different intensities of the exciting radiation 10¹⁰–10¹⁵ photons/cm²·s. Photoexcitation at 5.5 μm was realized using a semiconductor laser. At temperatures below 6 K and low bias voltages (<0.5 V) the current-voltage characteristics were found to have a threshold-like character. The threshold voltage rises as the temperature is lowered and the radiation intensity is increased. A model based on the Frenkel’-Poole effect in the impurity band has been developed. This model can be used to numerically describe the current-voltage characteristics with accuracy better than 5%. As a result, it is found that the photoconductivity rises and then reaches a plateau as the radiation intensity increases. Under these conditions, as under equilibrium conditions (in darkness), the hopping conductivity also depends exponentially on the electric field. This fact is explained in terms of the destruction by the electric field of (A ⁺-A ⁻) impurity complexes which appear under nonequilibrium conditions. Fiz. Tekh. Poluprovodn. 32, 192–199 (February 1998)     

InAsSbP double-heterostructure lasers for the spectral range 2.7–3.0 µm (T=77 K)

We have produced, by using liquid-phase epitaxy, 2.7 to 3.0-μm lasers based on InAsSbP double-heterostructures with different phosphorus contents in the active and wide-gap regions. The lasers possess threshold current density ∼0.8 kA/cm² at 77 K and operate in the pulsed mode up to ∼124 K with maximum threshold current density 10–12 kA/cm². The lasers have a low series resistance ∼0.45 Ω. Fiz. Tekh. Poluprovodn. 32, 241–244 (February 1998)     

Spatial beam oscillations in stripe lasers utilizing InAsSb/InAsSbP heterojunctions

Anomalously narrow, single-lobe and double-lobe beam directivity patterns in the plane of the p-n junction have been observed in lasers constructed from InAsSb/InAsSbP heterojunctions emitting at a wavelength of approximately 3.3 μm. Theoretical near-field and far-field radiation distributions for the laser emission of two beams oscillating across the stripe are obtained on the basis of new concepts of the lasing processes. The single-lobe directivity pattern is obtained for the emission of in-phase beams, and the double lobe is obtained for antiphase beams. Correspondence of the theory with experiment is established. Fiz. Tekh. Poluprovodn. 33, 1014–1019 (August 1999)     

Two-mode diode-laser spectroscopy with a InAsSb/InAsSbP laser near 3.6 µm

The current dependence of the output frequency of InAsSb/InAsSbP diode lasers at wavelengths near 3.6 μm is studied. It is found that in these lasers the number of lasing modes can be reduced without introducing crystallographic defects. It is shown that the photon momentum aids in suppressing the spectral modes closest to the dominant mode. Two-mode laser spectroscopy is done over an interval of 2 cm⁻¹ for two gases, N₂O and CH₃Cl. Fiz. Tekh. Poluprovodn. 33, 1469–1474 (December 1999)     

TE- and TM-polarized optoelectronic properties of HgCdTe quantum wells

A systematic investigation of the strength of TE-polarized and TM-polarized intersubband and interband transitions in narrow-gap HgCdTe quantum wells is performed using an eight-band finite-element k·p formalism. Effects of varying the well composition, well width, and applied electric field are explored for both polarizations, and the possibility of fabricating low-threshold quantum cascade lasers using this system is pointed out. Especially promising are the prospects for optically-pumped terahertz lasers based on interband transitions. Lasers emitting in the 30–45 μm wavelength range (falling in the phonon bands of III–V quantum wells), are projected to operate above liquid-nitrogen temperature.     

Properties of self-organized SiGe nanostructures formed by ion implantation

Properties of self-organized SiGe quantum dots formed for the first time by ion implantation of Ge ions into Si are studied using Auger electron spectroscopy, atomic-force microscopy, and scanning electron microscopy. It is found that a spatially correlated distribution of Ge atoms is observed in Si layers implanted with Ge ions after subsequent annealing of these layers. As a result, nanometer-sized regions enriched with germanium are formed; germanium concentration in these regions is 10–12% higher than that in the surrounding matrix of the SiGe solid solution. Optical properties of the layers with SiGe quantum dots were studied using Raman scattering and photoluminescence. An intense photoluminescence peak is observed in the wavelength region of 1.54–1.58 μm at room temperature. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 5, 2004, pp. 593–597. Original Russian Text Copyright ? 2004 by Parkhomenko, Belogorokhov, Gerasimenko, Irzhak, Lisachenko.     

Current and temperature tuning of quantum-well lasers operating in 2.0-to 2.4-µm range

Radiation spectra of GaInAsSb/GaAlAsSb-based quantum-well diode lasers in pulsed and quasi-continuous operation modes were studied in the temperatures range from −10 to +20°C with driving currents varying from 50 to 200 mA. For currents exceeding the threshold value by no more than 30%, a single-mode lasing was usually observed. A further increase in current leads, as a rule, to the appearance of 3–5 additional long-wavelength cavity modes, which suggests the growth of gain in this spectral range due to the interaction of modes. In single-mode conditions, the lasing wavelength is red-shifted with temperature at a rate of 2–3 ?/K because of the current-induced heating of the laser and the corresponding increase in the refractive index. The rate of this heating is estimated at 0.1 μs. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 4, 2003, pp. 502–507. Original Russian Text Copyright ? 2003 by Astakhova, Baranov, Viset, Imenkov, Kolchanova, Stoyanov, Chernyaev, Yarekha, Yakovlev.