Temperature-induced delocalization of excitations in GaAs/AlAs type-II superlattices

This paper describes investigations of the photoluminescence spectra of heterostructures containing short-period type-II GaAs/AlAs superlattices grown both within the regime where the heterojunction is smoothed, and in a regime where it is not smoothed, in the temperature range 10–40 K. A quantitative analysis of the experimental data shows that the quenching of exciton luninescence in the majority of cases is characterized by a single value of the activation energy E ₂=8±1 meV which coincides with the value of the binding energy of an X-Γ exciton. It is concluded that the primary reason for quenching in this temperature interval is thermal dissociation of the exciton into a pair of free carriers whose delocalization is accompanied by nonradiative recombination at traps. It is observed that smoothing the heterojunction leads to an increase in the probability of quenching by 1–2 orders of magnitude on the average. Fiz. Tverd. Tela (St. Petersburg) 40, 1140–1146 (June 1998)     

Temperature-Dependent Photoluminescence Analysis of 1.0 MeV Electron Irradiation-Induced Nonradiative Recombination Centers in n~+-p GaAs Middle Cell of GaInP/GaAs/Ge Triple-Junction Solar Cells

The effects of irradiation of 1.0 MeV electrons on the n~+-p GaAs middle cell of GaInP/GaAs/Ge triple-junction solar cells are investigated by temperature-dependent photoluminescence(PL) measurements in the 10-300 K temperature range. The appearance of thermal quenching of the PL intensity with increasing temperature confirms the presence of a nonradiative recombination center in the cell after the electron irradiation, and the thermal activation energy of the center is determined using the Arrhenius plot of the PL intensity.Furthermore,by comparing the thermal activation and the ionization energies of the defects, the nonradiative recombination center in the n~+-p GaAs middle cell acting as a primary defect is identified as the E5 electron trap located at E_c-0.96 eV.     

670 nm AlGaInP/GaInP strained multi-quantum well laser diode with high characteristic temperature (T 0)

A 670 nm AlGaInP/GaInP strained multi-quantum well laser diode with a high characteristic temperature (T ₀) has been achieved by optimization of quantum well structures and the metal-organic chemical vapour deposition process. The hole concentration of 5×10¹⁷ cm^-3 in the p-AlGaInP cladding layer on a (100) 5° off GaAs substrate has been obtained with very small ratio, 0.35, of mole flow rate of zinc source to the group III sources ([DEZn]/[III]) of 0.35. The threshold current and maximum temperature for continuous wave operation of lasers with cavity length of 300 m have been measured as 45 mA and 80°C, respectively. The characteristic temperature (T ₀) of the lasers has been measured as high as 153 K. The laser without facet protections could operate for more than 1000 h at 50°C and 5 mW.     

AlGaInP visible quantum well lasers for information technology

650 nm-range AlGaInP multi-quantum well (MQW) laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) have been studied and the results are presented in this paper. Threshold current density of broad area contact laser diodes can be as low as 350 A/cm². Laser diodes with buried-ridge strip waveguide structures were made, threshold currents and differential efficiencies are (22–40) mA and (0.2–0.7) mW/mA, respectively. Typical output power for the laser diodes is 5 mW, maximum output power of 15 mW has been obtained. Their operation temperature can be up to 90°C under power of 5 mW. After operating under 90°C and 5 mW for 72 hrs, the average increments for the threshold currents of the lasers at 25°C and the operation currents at 5 mW (at 25°C) are (2–3) mA and (3–5) mA, respectively. Reliability tests showed that no obvious degradation was observed after 1400 hours of CW operation under 50°C and 2.5 mW. Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998.     

Interband transition matrix element and temperature dependence of the lasing threshold for GaN laser structures

By comparing experimental and theoretical radiative recombination spectra, we have determined the values of the square of the matrix element for interband optical transitions |M|² in epitaxial GaN at different temperatures T. The data obtained were used to analyze the mechanism for the temperature dependence of the lasing threshold for a GaN laser. In the experiments, we used epitaxial layers of GaN with a wurtzite crystal structure, grown on Al₂O₃ (0001) substrates and excited by a focused beam from a nitrogen laser. We have shown that the spontaneous emission spectra near the lasing threshold of a GaN laser are consistent with the model of optical interband transitions not obeying a selection rule for the electron wave vector. As we have established, the parameter |M|² practically does not vary for T = 300–470 K: 5.4·10⁻⁷³ kg²·m⁵/sec². Further increase in the temperature leads to an exponential fall-off in |M|² down to 3.4·10⁻⁷³ kg²·m⁵/sec² at T ≈ 520 K. Such behavior of |M|² as a function of temperature correlates with the sudden increase in the nonradiative recombination rate at T > 470 K, and may be connected with a change in the recombination mechanisms in the active layer of the GaN laser in the high temperature region. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 790–794, November–December, 2007.     

Analysis of anticipated performance of 650-nm GaInP/AlGaInP quantum-well GaAs-based VCSELs at elevated temperatures

The possibility of application of the 650-nm oxide-confined GaInP/AlGaInP quantum-well vertical-cavity surface-emitting diode lasers (VCSELs) at elevated temperatures as sources of the carrier 650-nm wave in the fibre optical communication using POFs has been investigated with the aid of the comprehensive self-consistent model. An increase in the VCSEL threshold current at higher temperatures has been found to be mostly associated with both the carrier leakage from the valley of the Ga_0.43In_0.57P quantum-well material to the X-valley of the (Al_0.67Ga_0.33)_0.52In_0.48P barriers and the band-to-band absorption within the Ga_0.52In_0.48P layer of the band-gap comparable with the energy of emitted radiation. Nevertheless, the AlGaInP VCSELs exhibit encouraging thermal behaviour with the characteristic temperature T₀ equal to as much as 134 K for the active-region temperatures up to 357 K. For the 5-μm devices, the maximal achievable output has been determined to decrease from a quite high value of 1.0 mW for 293 K to 0.6 mW for 320 K and to still high 0.33 mW for 340 K. However, an efficient operation of the above VCSEL at elevated temperatures requires still some structure modifications leading to a reduction of both the above effects, the electron leakage from the valley and the band-to-band absorption within GaInP layers.     

Investigation of temperature characteristics of modern InAsP/InGaAsP multi-quantum-well TJ-VCSELs for optical fibre communication

Continuous-wave (CW) performance of modern 1.3-μm InAsP/InGaAsP multi-quantum-well (MQW) tunnel-junction vertical-cavity surface-emitting diode lasers (TJ-VCSELs) is investigated using our comprehensive self-consistent simulation model to suggest their optimal design for room and elevated temperatures. For increasing ambient temperatures, an increase in the VCSEL threshold current has happened to be mostly associated with the Auger recombination. Nevertheless, the InAsP/InGaAsP VCSELs have been found to exhibit encouraging thermal behaviour with the quite high value of maximal operating temperature of 350 K. It has been found that 5-μm devices seem to be the most optimal ones because they demonstrate both the room temperature (RT) threshold current equal to only 0.55 mA and maximum operating temperature equal to as much as 345 K. For these devices, the characteristic temperature T0 is equal to 92 K for 290–305 K, 51 K for 310–325 K and 29 K for 330–345 K. Therefore, the InAsP/InGaAsP VCSELs have been found to offer very promising performance both at room and elevated temperatures as sources of the carrier 1.3-μm wave in the fibre optical communication using silica fibres.     

Carrier Dynamics and Saturation Effect in (113)B InAs/InP Quantum Dot Lasers

Quantum dot (QD) lasers exhibit many interesting and useful properties such as low threshold current, temperature insensitivity or chirpless behavior. In order to reach the standards of long-haul optical transmissions, 1.55 μm InAs QD lasers on InP substrate have been developed. Based on time resolved photoluminescence (PL) measurements, carrier dynamics behavior is at first investigated. Electroluminescence (EL) results are then shown at room temperature exhibiting a laser emission centered at 1.61 μm associated to a threshold current density as low as 820 A/cm² for a six InAs QD stacked layers. Finally, a rate equation model based on the reservoir theory is used to model both time-resolved photoluminescence (TRPL) and electroluminescence results. It is shown that carrier dynamic calculations are in a good agreement with measurements since the saturation effect occurring at high injected power is clearly predicted. P. Miska: Previously at Laboratoire d’Etude des Nanostructures à Semiconducteurs.     

Optimising dislocation-engineered silicon light-emitting diodes

This article presents a study of the possibilities of optimising the electroluminescence (EL) efficiency of dislocation-engineered silicon light-emitting diodes (DELEDs). The diodes were produced by implantation of boron in n-type (100)Si wafers, at a constant ion energy and fluence, of 30 keV and 1×10¹⁵ ions/cm², respectively. The density and the areal coverage by dislocation loops were varied by applying different annealing times in a rapid thermal processing, from 30 s to 60 min. It is shown that the EL efficiency is directly correlated to the number and areal coverage by the loops. The highest population of loops, ∼5×10⁹ /cm², and an areal coverage of around 50% were achieved for 1–5 min annealing. This loop distribution results in optimal DELEDs, having the highest EL response and the largest increase of EL intensity with operating temperature (80–300 K). The results of this work confirm a previously introduced model of charge-carrier spatial confinement by a local stress induced by the edge of the dislocation loops, preventing carrier diffusion to non-radiative recombination centres and enhancing radiative transitions at the silicon band edge. PACS 85.60.Jb; 78.60.Fi; 61.72.Tt     

退火对AlGaInP/GaInP多量子阱 LED外延片性能的影响

采用LP-MOCVD技术在n-GaAs衬底上生长了AlGaInP/GaInP多量子阱红光LED外延片.研究表明退火对外延片性能有重要影响.与未退火样品相比,460℃退火15min,外延片p型GaP层的空穴浓度由5.6×10¹⁸cm^-3增大到6.5×10¹⁸cm^-3,p型AlGaInP层的空穴浓度由6.0×10¹⁷cm^-3增大到1.1×10¹⁸cm^-3.但退火温度为780℃时,p型GaP层和p型AlGaInP层的空穴浓度分别下降至8×10¹⁷cm^-3和1.7×10¹⁷cm^-3,且Mg原子在AlGaInP系材料中的扩散加剧,导致未掺杂AlGaInP/GaInP多量子阱呈现p型电导.在460～700℃退火范围内,并没有使AlGaInP/GaInP多量子阱的发光性能发生明显变化.但退火温度为780℃时,AlGaInP/GaInP多量子阱的发光强度是退火前的2倍.     

Charge transfer mechanism in high-purity silicon-basedn +-π-p + structures

Results of experimental investigations into current-voltage characteristics of n⁺-π-p⁺ structures based on high-purity silicon doped with boron are presented. It is shown that the I–V characteristic at high injection levels is described by Stafeev's theory, when the thickness d of the π-region is smaller than or close to three ambipolar diffusion lengths L_a. For a current density J above (3–50) A/cm² at varying temperatures, the I–V characteristic obeys a relation usually occurring in the case where charge-carrier recombination in the n⁺ and p⁺-regions dominates that found in the π-region. The effect of mutual electron-hole scattering on the behavior of the I–V characteristic is evident at J>630 A/cm³. For d/L_a=9, the I–V characteristic at high injection levels is treated by the theory of double carrier injection into a semiconductor with consideration for diffusion corrections. In the temperature range below 200–276 K, the I–V curve for all samples studied exhibits a linear dependence on J followed by a portion corresponding to a maximum occupancy of recombination levels by injected electrons. Here the Fe or Au donor levels presumably act as recombination levels. The electron and hole capture areas (cross sections) by recombination centers are roughly estimated. Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 35–45, July 2000.     

深能级对AlGaInP/GaAs异质结双极晶体管性能的影响

用深能级瞬态光谱和光致发光(PL)方法研究了AlGaInP/GaAs异质结双极晶体管(HBT)发射区AlGaInP中的深能级.得到了两个深能级,分别为E_c-E_t1＝0.42eV和E_c-E_t2＝0.59eV,其复合截面为σ_n1＝6.27×10^-17cm²和σ_n2＝6.49×10^-20cm². 关键词：     

Enhanced single-fundamental LP01 mode operation of 650-nm GaAs-based GaInP/AlGaInP quantum-well VCSELs

Minimal optical attenuation of plastic (polymer) optical fibres (POFs) corresponds to the 650-nm wavelength. Currently the GaInP/AlGaInP quantum-well (QW) oxide-confined (OC) vertical-cavity surface-emitting diode lasers (VCSELs) are undoubtedly the laser devices most suited to be used in 650-nm POF optical communication, for which the stable single-fundamental-mode LP₀₁ emission (SFM) is definitely the one most desired. In the present paper, the comprehensive fully self-consistent VCSEL model is used to examine mode selectivity of the above VCSELs. An increase in the VCSEL active-region diameter leads to a gradual modification of the current injection into this region and subsequent carrier radial diffusion within it before their recombination, which is followed by an essential transformation of active-region optical-gain profiles deciding upon an excitation of successive transverse modes. In standard arsenide OC VCSELs, SFM operation is usually limited to relatively small active regions. But for a room-temperature continuous-wave operation of the GaInP/AlGaInP VCSELs, the fundamental LP₀₁ mode remains surprisingly the lowest-threshold one up to relatively large active regions of 9-μm diameters. Nevertheless, in such VCSELs, thresholds of many LP modes become very similar to one another, which leads to their relatively poor mode selectivity and an unwanted multi-mode operation for higher output powers.     

Thermophysical properties of PLZT ferroelectric ceramics with a nanopolar structure

The heat capacity, thermal expansion coefficient, and deformation of the PLZT-9/65/35 compound are studied in the temperature range 150–800 K. Diffuse anomalies are detected in the temperature dependences of the heat capacity and thermal expansion coefficient over wide temperature ranges of 250–650 and 330–550 K, respectively. The anomalous behavior of the heat capacity in the temperature range 250–650 K is shown to be caused by the appearance of two-level states (Schottky anomaly). The results obtained are discussed along with the data of structural and dielectric studies.     

Temperature‐dependent electroluminescence intensity in green and blue (In,Ga)N multiple‐quantum‐well diodes

The electroluminescence (EL) intensity has been investigated of green and blue (In,Ga)N multiple‐quantum‐well diodes grown on c ‐plane sapphire over a wide temperature range and as a function of current between 0.01 mA and 10 mA. The EL intensity of the green diode with p‐(Al,Ga)N electron blocking layer does not show low‐temperature quenching, especially at low injection levels, previously observed for the blue (In,Ga)N quantum‐well diodes. This finding rules out possi‐ bilities that the freeze‐out of holes at deep Mg acceptor levels and the failure of hole injections through the p‐(Al,Ga)N layer are directly responsible for the EL quenching at temperatures below 100 K. Variations of the EL efficiency with current level suggest that capture/escape efficiencies of injected carriers by the wells play an important role for the determination of EL external quantum efficiency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sustained oscillations in GaInP/AlGalnP visible diode lasers

We report the observation of sustained oscillations and pulsation behaviour in various GaInP/AlGaInP 670 nm diode lasers. We present experimental dependences of the oscillation strength and frequency as functions of diode structure, temperature and drive current. We explore the resonant excitation of this oscillation using both an r.f. current signal and a tunable-repetition-rate picosecond laser source. When a diode laser with a weak internal oscillation is coupled to an external cavity, strong pulsing behaviour is observed, and we attribute this behaviour to self-mode-locking.     

Amplified luminescence and threshold current temperature dependencies of ZnSe and GaN laser diodes

Using a transfer equation approach, it is shown that the cavity-trapped amplified luminescence (AL) flux densities S integrated over the frequency and cavity length at the threshold of ZnSe, zinc-blende and wurtzite GaN laser diodes (LDs) with stripe-geometry bulk active layers reach (3.5–9)×10⁴ MW/m² within the temperature range 200–400 K. At these values of S, the nonlinear optical effects induced by AL can be observed. The AL induced recombination can enhance the threshold current density of the short wavelength LDs by two or even three times. Received: 7 January 2002 / Revised version: 11 April 2002 / Published online: 8 August 2002     

Electroluminescence (at 316 nm) and electrical stability of a MOS light-emitting device operated at different temperatures

The influence of the operating temperature on the electrical and optical stability of the Metal–Oxide–Silicon-based light-emitting device (MOSLED) with Gd and Gd plus K implanted SiO₂ layers was investigated. An increase of the temperature from room temperature up to 423 K reduces the gate voltage by about 8 V due to the Auger de-excitation mainly. It increases the rate of the EL quenching process and the degradation of the MOSLED structure by a factor of three. On the other hand, the MOSLED structure containing Gd and K atoms shows that an increase of the operating temperature leads to a threefold decrease of the decay time what was not observed in the gadolinium-implanted sample. The decrease of the operating temperature down to 70 K leads to an increase of the EL intensity and the operating time in both cases.     

Temperature dependence of electroluminescence from Si-based light emitting diodes with β-FeSi2 particles active region

Electroluminescence (EL) properties of Si-based light emitting diodes with β-FeSi₂ particles active region grown by reactive deposition epitaxy are investigated. EL intensity of β-FeSi₂ particles versus excitation current densities has different behaviors at 8, 77 K and room temperature, respectively. The EL peak energy shifted from 0.81 to 0.83 eV at 77 K with the increase of current density from 1 to 70 A/cm². Temperature dependence of the peak energy can be well fitted by semi-empirical Varshni's law with the parameters of α=4.34 e-4 eV/K and β=110 K. These results indicate that the EL emission originates from the band-to-band transition with the band gap energy of 0.824 eV at 0 K.     

Effect of alkali-metal doping on photoluminescence of CdS films

It is established that doping of CdS polycrystalline films with alkaline metals (Li, Na, K, Cs) results in an increase of luminescence intensity by 3–5 times compared with pure films. This increase is accounted for by the placement of alkaline-metal ions in V _Cd ²⁻ cation vacancies, which are nonradiative recombination centers in these films. From the dependences of the luminsecence intensity of the doped films on the synthesis conditions (deposition temperature, concentration of doping impurities, type of doping metal), the parameters that ensure the maximum luminescence intensity of the films are determined as T_dep ≈ 450°C and C_Me = 1·10⁻⁵ at %. The luminescence intensity decreases by 1–3% upon exposure of the films to UV light (λ_max = 365 nm, I = 10²¹ quanta·sec·cm⁻¹) for several hours. This is indicative of the stability of these films against UV radiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii Vol. 74, No. 3, pp. 362–366, May–June, 2007.