Superlinear electroluminescence in GaSb-based heterostructures with high potential barriers

The electroluminescence in isotype and anisotype light-emitting diode heterostructures grown by the method of liquid-phase epitaxy with large conduction-band offset ΔE _c at the heterointerface between a narrow-band active region and a wide-band layer is studied. Two types of electroluminescence peaks are observed in the range of photon energies 0.28–0.74 eV at temperatures T = 300 and 77 K; in this case, a super-linear increase in the intensity and optical power of emission by a factor of 1.5–2 is observed in the range of pump currents 20–220 mA. This effect is attributed to the formation of additional electron-hole pairs as a result of impact ionization by hot electrons heated as a result of the band offset ΔE _c in the conduction band at the n-AlGaAsSb/n-InGaAsSb and n-GaSb/n-InGaAsSb heteroboundaries. This effect can be used to increase the quantum efficiency of semiconductor emitters (light-emitting diodes, lasers) in the mid-infrared region.     

Features of high-temperature electroluminescence in an LED <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-InGaAsSb/<Emphasis Type="Italic">p</Emphasis>-AlGaAsSb heterostructure with high potential barriers

The electroluminescent properties of a light-emitting diode n-GaSb/n-InGaAsSb/p-AlGaAsSb heterostructure with high potential barriers are studied in the temperature range of 290–470 K. An atypical temperature increase in the power of the long-wavelength luminescence band with an energy of 0.3 eV is experimentally observed. As the temperature increases to 470 K, the optical radiation power increases by a factor of 1.5–2. To explain the extraordinary temperature dependence of the radiation power, the recombination and carrier transport processes are theoretically analyzed in the heterostructure under study.     

Temperature dependence of the threshold current of QW lasers

The temperature dependence of the threshold current in GaInAs-based laser structures has been studied in a wide temperature range (4.2 ≤ T ≤ 290 K). It is shown that this dependence is monotonic in the entire temperature interval studied. Theoretical expressions for the threshold carrier density are derived and it is demonstrated that this density depends on temperature linearly. It is shown that the main contribution to the threshold current comes from monomolecular (Shockley-Read) recombination at low temperatures. At T > 77 K, the threshold current is determined by radiative recombination. At higher temperatures, close to room temperature, Auger recombination also makes a contribution. The threshold current grows with temperature linearly in the case of radiative recombination and in accordance with T ³ in the case of Auger recombination.     

A study of n +-6H/n-3C/p +-6H-SiC heterostructures grown by sublimation epitaxy

The n ⁺-6H/n-3C/p ⁺-6H-SiC structure was fabricated for the first time by sublimation epitaxy, with mesa diodes formed on its base and their electrical characteristics were studied. It was found that a green band dominates in the spectrum of injection electroluminescence (EL) of these diodes. The band is close by its parameters to that associated with free-exciton recombination in bulk 3C-SiC, but is shifted by ～0.06 eV to shorter wavelengths. A similar effect was observed previously for triangular quantum wells in an n ⁺-6H-SiC/p-3C-SiC heterojunction. An analysis of the experimental data obtained demonstrated that the structure can be regarded as two independent heterojunctions. The EL spectrum observed may be associated with radiative recombination at the n ⁺-6H-SiC/n-3C-SiC heterointerface.     

Unusual temperature dependence of electroluminescence intensity in blue InGaN single quantum well diodes

Temperature dependence of electroluminescence (EL) spectral intensity of the super-bright blue InGaN single quantum well (SQW) light emitting diodes (LEDs) has been carefully investigated over a wide temperature range (T=15-300 K) and as a function of injection current level (0.1-10 mA) in comparison with high quality GaAs SQW-LEDs. When T is slightly decreased to 180 K, the EL intensity efficiently increases in both cases due to the reduced non-radiative recombination processes. However, further decreasing T below 100 K, striking differences exist in EL intensity as well as injection current dependences between the two types of diodes. That is, the EL efficiency at lower T is found to be quite low for the blue diode in strong contrast to that of red GaAs SQW-LED where significant enhancement of the EL efficiency persists down to 15 K. These results indicate that the carrier capture efficiency of the blue SQW diode is unusually worse at lower T than at T=180-300 K, reflecting the unique radiative recombination processes under the presence of high-density dislocation (10¹⁰ cm⁻²).     

High-efficiency LEDs based on <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">p</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb/<Emphasis Type="Italic">P</Emphasis>-AlGaAsSb type-II thyristor heterostructures

A new type of light-emitting diodes (LEDs), a high-efficiency device based on an n-GaSb/p-GaSb/n-GaInAsSb/P-AlGaAsSb thyristor heterostructure, with the maximum emission intensity at wavelength λ = 1.95 μm, has been suggested and its electrical and luminescent characteristics have been studied. It is shown that the effective radiative recombination in the thyristor structure in the n-type GaInAsSb active region is provided by double-sided injection of holes from the neighboring p-type regions. The maximum internal quantum efficiency of 77% was achieved in the structure under study in the pulsed mode. The average optical power was as high as 2.5 mW, and the peak power in the pulsed mode was 71 mW, which exceeded by a factor of 2.9 the power obtained with a standard n-GaSb/n-GaInAsSb/P-AlGaAsSb LED operating in the same spectral range. The approach suggested will make it possible to improve LED parameters in the entire mid-IR spectral range (2–5 μm).     

Photoelectric and luminescence properties of GaSb-Based nanoheterostructures with a deep Al(As)Sb/InAsSb/Al(As)Sb quantum well grown by metalorganic vapor-phase epitaxy

The luminescence and photoelectric properties of heterostructures with a deep Al(As)Sb/InAsSb/Al(As)Sb quantum well grown on n-GaSb substrates by metalorganic vapor-phase epitaxy are investigated. Intense superlinear luminescence and increased optical power as a function of the pump current in the photon energy range of 0.6–0.8 eV are observed at temperatures of T = 77 and 300 K. The photoelectric, current-voltage, and capacitance characteristics of these heterostructures are studied in detail. The photosensitivity is examined with photodetectors operating in the photovoltaic mode in the spectral range of 0.9–2.0 μm. The sensitivity maximum at room temperature is observed at a wavelength of 1.55 μm. The quantum efficiency, detectivity, and response time of the photodetectors were estimated. The quantum efficiency and detectivity at the peak of the photosensitivity spectrum are as high as η = 0.6–0.7 and D _λmax ^* = (5–7) × 10¹⁰ cm Hz^1/2 W^?1, respectively. The photodiode response time determined as the rise time of the photoresponse pulse from 0.1 to the level 0.9 is 100–200 ps. The photodiode transmission bandwidth is 2–3 GHz. Photodetectors with a deep Al(As)Sb/InAsSb/Al(As)Sb quantum well grown on n-GaSb substrates are promising foruse in heterodyne detection systems and in information technologies.     

Special features of spontaneous and coherent emission of IR lasers based on a single type-II broken-gap heterojunction

The electroluminescence characteristics of a single type-II p-Ga_0.84In_0.16As_0.22Sb_0.78/n-In_0.83Ga_0.17As_0.80Sb_0.20 heterostructure have been studied in the temperature range 77–300 K. A new advanced laser structure based on a type-II broken-gap p-GaInAsSb/n-InGaAsSb heterojunction as the active region has been suggested and fabricated. Single-mode lasing at wavelength λ=3.14 µm under a threshold current density j_th=400 A/cm² (T=77 K) was obtained. The domination of TM-over TE-polarization, observed both in the spontaneous and coherent modes of operation of the novel laser structure, can be accounted for by involvement of light holes, tunneling across the heterointerface, in radiative recombination.     

Electroluminescence in a semimetal channel at a single type II broken-gap heterointerface

The radiative recombination at the broken-gap p-GaInAsSb/p-InAs type-II interface is investigated in the temperature range of 4–100 K. It is shown that the electroluminescence band hν_A=0.37 eV can be attributed to a large extent to the recombination of electrons from the semimetal channel at the interface with the participation of a deep acceptor level at the interface. At the same time, the band hν_B=0.40 eV corresponds to radiative transitions in the InAs bulk to a shallow acceptor level. The participation of the interface states in the recombination across the GaInAsSb/InAs type-II interface becomes appreciable due to the overlapping of wave functions of holes, which are localized at the interface on the solid-solution side, with the wave functions of deep acceptor states.     

Photoconductivity and luminescence of CuInSe2 single crystals at a high level of optical excitation

The luminance-current and spectral characteristics of photoluminescence of the CuInSe₂ single crystals are studied. The superlinear portion of the excitation-intensity dependence of photoconductivity at low excitation intensities in compensated p-CuInSe₂ crystals is explained on the basis of a recombination model. The emission band that peaked at 0.98 eV in the n-CuInSe₂ photoluminescence spectrum corresponds to radiative recombination of electrons at the donor level with a depth of 0.04 eV. The maximum in the band intensity corresponds to the energy gap between the trap level and the valence band.     

Temperature-dependent current-voltage characteristics of Cr/n-GaAs Schottky diodes

The Cr/n-GaAs/In Schottky contacts have been formed using dc magnetron sputtering. The current-voltage (I-V) characteristics of the device have been measured by steps of 20 K in the temperature range of 60-320 K. The ideality factor n of the device has remained about unchanged between 1.04 and 1.10 and Schottky barrier height around 0.58-0.60 eV from 320 K down to 160 K. It can be said that the experimental I-V data are almost independent of temperature above 160 K. After 160 K, the n value increased with a decrease in temperature and become 1.99 at 60 K. The I-V characteristics at high temperatures have been exactly explained by the standard TE model. The nature and origin of abnormal behaviors at low temperatures have been successfully explained by the current flow through the low SBH circular patches suggested by Tung and used by some studies in literature. It has been seen that the straight line of the nT vs. T plot with a T₀ value of 14 K was parallel to that of the ideal Schottky contact. Again, a lateral homogeneous BH value of 0.62 eV was calculated from the linear relationship between the ideality factor and barrier height values. It has been seen that he ?(T = 0) and BH temperature coefficient α values obtained from the flat band BH and the Norde’s model plots are in close agreement with each other.     

Magneto-photoluminescence in a type-II broken-gap n-GaInAsSb/p-InAs heterojunction

Magneto-photoluminescence in a single type-II broken-gap n-Ga_0.94In_0.06As_0.13Sb_0.87/p-InAs heterostructure with a 2D electron channel at the heterointerface containing two occupied electron subbands has been studied in the spectral range 0.3–0.8 eV in high magnetic fields of up to 10 T at low temperatures (T = 7 K). At photon energies in the range 0.5–0.8 eV, bulk photoluminescence from the layer of the n-GaInAsSb alloy was observed. In the low-energy part of the spectrum (0.3–0.45 eV), three narrow emission bands with photon energies hν _a = 0.419 eV, hν _b = 0.404 eV, and hν _c = 0.384 eV and full widths at half-maximum FWHM = 4–7 meV were observed. These bands are due to radiative transitions of 2D electrons localized in the quantum well on the InAs side near the type-II heterointerface. The electron effective mass in the occupied subband E ₂ was estimated to be m ₂ = 0.027m ₀, which is close to the effective mass at the bottom of the InAs conduction band.     

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.     

Specific features of recombination processes in CdTe films produced in different temperature conditions of growth and subsequent annealing

The steady-state and kinetic characteristics of photoconductivity and photoluminescence and the thermally stimulated conductivity spectra of the GdTe layers deposited by vacuum evaporation onto heated substrates are studied in relation to the substrate temperature. The measurements are carried out at temperatures, illuminations, and wavelengths ranging from 4.2 to 400 K, from 10¹⁰ to 10²³ photon/cm², and from0.4 to 2.5 μm, respectively. A certain optimal range of substrate temperatures T _s ≈ 450–550°C, at which the as-prepared layers exhibit a high resistivity, a high photosensitivity, and the best structural quality, is established. In the spectra of these layers, a new luminescence band at hv _m = 1.09 eV is observed along with the known photoluminescence band at hv _m = 1.42 eV. It is established that this new band is due to intracenter transitions rather than recombination transitions. The nature of radiative recombination centers in the layers is discussed. It is suggested that the d electrons of cations can be involved in the formation of chemical bonds of local centers in CdTe.     

Polarization-resolved photoluminescence piezospectroscopy of GaAs/Al0.35Ga0.65As:Be quantum wells

The photoluminescence (PL) of GaAs/Al_0.35Ga_0.65As:Be quantum wells is studied at temperatures of 77 and 300 K under conditions of uniaxial compression along the [110] direction. There are two main lines in the PL spectra; at zero pressure and T = 77 K, the peaks appear at 1.517 and 1.532 eV. Comparison of the pressure dependences of the peak positions and the polarization of the PL measured experimentally with those calculated theoretically gives evidence that, at T ≥ 77 K, these bands originate from the recombination of free electrons with heavy and light holes in the GaAs valence band.     

Characterization of radiative efficiency in double heterostructures of InGaAsP/InP by photoluminescence intensity analysis

The photoluminescence (PL) intensity of an InGaAsP layer has been investigated as a function of excitation power density over a wide range of five orders. Two samples with n-InP/n-InGaAsP isotype and p-InP/n-InGaAsP heterotype doping have quite different excitation power dependences on PL intensity. The heterotype sample has notable nonlinear dependence. The excitation power dependences of PL intensity are theoretically analyzed. The estimated interface recombination velocity of the InP/InGaAsP heterojunction is found to be very low (smaller than a few cm/sec), compared with that of a GaAs/GaAlAs heterojunction.This PL intensity analysis has been applied to study the effect of an InP buffer layer and thermal degradation of radiative efficiency. The effective non-radiative recombination life time has been estimated as about 2×10⁻⁹ s for the double heterostructure with no buffer layer. Annealing in conditions of low phosphorus pressure leads to degradation of radiative efficiency, and the degradation is attributed to decrease in the nonradiative life time in the quaternary layer rather than increase in the interface recombination velocity. Sufficient phosphorus pressure prevents degradation of radiative efficiency. The correlation between PL intensity and output optical power of the light emitting diode has also been investigated. The PL intensity must be measured at high excitation power if it is to accurately predict the output power as a light emitting diode.     

Quantum-confinement effect in silicon-on-insulator films implanted with high doses of hydrogen ions

280-nm-thick silicon-on-insulator films are implanted with high doses of hydrogen with the energy 24 keV and the dose 5 × 10¹⁷ cm^?2. Peaks corresponding to optical phonons localized in the silicon nanocrystals 1.9?C2.5 nm in size are observed in the Raman spectra. The fraction of the nanocrystal phase is ??10%. A photoluminescence band with a peak at about 1.62 eV is detected. The intensity of the 1.62 eV band nonmonotonically depends on the measurement temperature in the range from 88 to 300 K. An increase in the radiative recombination intensity at temperatures <150 K is interpreted in the context of a two-level model for the energy of strongly localized electrons and holes. The activation energy of photoluminescence enhancement is 12.4 meV and corresponds to the energy of splitting of the excited state of charge carriers localized in the silicon nanocrystals.     

Relaxation of photoexcited silver chloride

Relocalization of excess carriers from shallow levels to deep levels is observed in addition to carrier recombination during thermal relaxation of photoexcited silver chloride. Experimental dependences of the parameters of the photostimulated luminescence flash (released light sum and kinetic coefficient) on the relaxation time and temperature are explained within a three-level model including a recombination (luminescence) level, a deep level with energy ΔE ≈ 1.8 eV, and a shallow level with energy ΔE ≈ 0.03 eV with respect to the conduction-band bottom. It was shown that Ag⁺ ion adsorption caused a decrease in the relocalization activation energy from 0.17 to 0.03 eV, which is attributed to the surface nature of the centers responsible for the initial relaxation stage.     

Photoluminescence of Ga1−x InxAsySb1−y solid solutions lattice-matched to InAs

Photoluminescence of Ga_1?x In _x As _y Sb_1?y (0.08<x<0.22) epilayers lattice-matched to InAs substrate was investigated for the first time at 80 K, and the band gap of solid solutions was evaluated experimentally. It was demonstrated that the intensity of the band-to-band radiative recombination for p-GaInAsSb undoped layers depends on the composition of the quaternary solid solution and is governed by the concentration of intrinsic structural defects. For an n-GaInAsSb:Te donor-doped layer, the band-to-band recombination band and an additional emission band were observed. The latter band is related to the radiative recombination via the deep acceptor level formed by an intrinsic complex V _GaTe with the activation energy E _DA =122 meV.     

Luminescence of porous silicon in the infrared spectral region at room temperature

A method for preparing mesoporous silicon on n-type substrates has been developed. The material exhibits two intense bands of photo-and electroluminescence at room temperature: a primary one in the range 1.4–1.8 eV, and a low-energy infrared band near 1–1.2 eV. It is shown that the position of the primary emission maximum and the intensity of the band can be controlled. The properties of the primary band are explained in terms of a quantumsize model for formation of porous silicon, while the low-energy band is explained as radiative recombination in larger non-quantum-size crystallites. Fiz. Tekh. Poluprovodn. 31, 365–369 (March 1997)