Nonradiative Recombination Mechanisms Research Articles

Frequency Dependence of Drain Conductance due to Hole Accumulation in InAlAs/InGaAs High Electron Mobility Transistors

The frequency dependencies of the drain conductance (Gd) and the responsivity of InAlAs/InGaAs high electron mobility transistors were investigated using a network analyzer. The Gd exhibited the same frequency dependence as responsivity under 1.3-µm-wavelength laser illumination, indicating that the frequency dependence of Gd arises from the recombination of holes that have accumulated in the source region with the two-dimensional electron gas (2DEG). The holes were generated in the drain region by impact ionization under the strong electric field and drifted toward the source region. The drain conductance due to impact ionization can be expressed as Lorentz frequency dependence with f3dB being the 3-dB-down frequency. The minority carrier (hole) lifetime, τ, was estimated using the relation 1/2 πf3dB. The frequency dependence of Gd at several drain-to-source and gate-to-source voltages was investigated. The recombination lifetime for a system in which both electrons and holes co-exist was theoretically estimated, taking account of self-consistent solutions of both the Schrödinger and Poisson equations and the nonradiative Auger recombination mechanism. The experimental and theoretically estimated results clearly show that the frequency dependence of Gd is caused by the accumulation of holes in the source region and their recombination with the 2DEG. Based on the experimental and theoretical results, the distribution of holes in the channel and the multiplication factor due to the impact ionization are discussed in details.

Recombination and loss mechanisms in low-threshold InAs-GaAs 1.3-/spl mu/m quantum-dot lasers

We show that even in quantum-dot (QD) lasers with very low threshold current densities (J/sub th/=40--50 A/cm/sup 2/ at 300 K), the temperature sensitivity of the threshold current arises from nonradiative recombination that comprises /spl sim/60% to 70% of J/sub th/ at 300 K, whereas the radiative part of J/sub th/ is almost temperature insensitive. The influence of the nonradiative recombination mechanism decreases with increasing hydrostatic pressure and increasing band gap, which leads to a decrease of the threshold current. We also studied, for the first time, the band gap dependence of the radiative part of J/sub th/, which in contrast increases strongly with increasing band gap. These results suggest that Auger recombination is an important intrinsic recombination mechanism for 1.3-/spl mu/m lasers, even in a very low threshold QD device, and that it is responsible for the temperature sensitivity of the threshold current.

Mechanisms of radiative and nonradiative recombination in ZnSe:Cr and ZnSe:Fe

Possible applications of ZnSe:Cr in optoelectronics are discussed. It is shown that 2+ to 1+ photo-ionization of chromium results in efficient pumping of Cr2+ intrashell emission and in energy up-conversion from green to blue. A distinct difference in efficiency of the energy up-conversion is observed between chromium- and iron-doped ZnSe samples. This difference we relate to a very efficient Auger mechanism of photoluminescence quenching in Fe-doped samples. We further demonstrate an anticorrelation of the intensities of mid-infrared Cr emission and up-converted blue emission of ZnSe.

DLTS properties of iron defects in crystalline silicon used in solar cells

Crystalline silicon used in solar cells has been investigated using deep level transient spectroscopy (DLTS). In majority-carrier pulse sequence an interstitial iron deep level was observed. However, the investigation of this deep level peak with different filling pulsewidths shows that this level consists of two superimposed levels. The activation energies of these levels are 375 meV ( F 1 ) and 480 meV ( F 2 ). The capture cross section of the level ( F 1 ) with the lower activation energy is nearly two orders of magnitude larger than the capture cross section of defect F 2 . Both capture cross sections show, over a wide range, no temperature dependence indicating that nonradiative recombination mechanisms other than multiphonon emission are involved. The concentration ratio between both defects is nearly 1:2.

DLTS properties of iron defects in crystalline silicon used in solar cells

Crystalline silicon used in solar cells has been investigated using deep level transient spectroscopy (DLTS). In majority-carrier pulse sequence an interstitial iron deep level was observed. However, the investigation of this deep level peak with different filling pulsewidths shows that this level consists of two superimposed levels. The activation energies of these levels are 375 meV ( F 1) and 480 meV ( F 2). The capture cross section of the level ( F 1) with the lower activation energy is nearly two orders of magnitude larger than the capture cross section of defect F 2. Both capture cross sections show, over a wide range, no temperature dependence indicating that nonradiative recombination mechanisms other than multiphonon emission are involved. The concentration ratio between both defects is nearly 1:2.

Temperature dependence of photoluminescence intensity from AlGaInP/GaInP multi-quantum well laser structures

AlGaInP/GaInP multiple quantum well laser structure was grown by low-pressure metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine. Photoluminescence (PL) measurements were performed from 10 to 230 K. The PL energy increased with temperature from 10 to 70 K and decreased above 70 K. The former was attributed to thermal activation of trapped carriers due to localization in the quantum wells, while the latter was attributed to temperature-induced band-gap shrinkage. The PL intensity as a function of temperature was fitted by employing two nonradiative recombination mechanisms with good agreement, resulting in two activation energies that correspond to losses of photogenerated carriers to nonradiative centers.

Recombination Mechanism in Short-Wavelength GaN/AlGaN Quantum Wells

ABSTRACTTo date, light emission by AlGaN-based heterostructures and LED's operating in the ultraviolet region is far less efficient than emission from longer wavelength structures based on GaInN. We have realized GaN/AlGaN quantum well structures emitting in the 360–320 nm range with peak room-temperature internal efficiencies reaching more than 20 %. From detailed studies of the temperature and excitation power dependence of the efficiency we find that excitons play a crucial role enhancing radiative recombination in such structures. Except for the peak internal efficiency, which reaches 73 % in GaInN/GaN, the overall behavior in GaN/AlGaN and GaInN/GaN is very similar, suggesting that the main difference is the nonradiative recombination mechanism.

Auger recombination involving dislocations in semiconductors

Auger capture of majority carriers by a charged edge dislocation in n-type semiconductorsis considered in the case of weak saturation of the dangling bonds existing on thedislocation core. The dependence of the capture radius on the depth of the one-dimensionaldislocation band and on temperature is obtained. Values of temperature and free electronconcentration are estimated when Auger capture is the dominant mechanism ofnonradiative recombination in crystals with dislocations.

Temperature-dependent photoluminescence of GaInP/AlGaInP multiple quantum well laser structure grown by metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine

A GaInP/AlGaInP multiple quantum well laser structure was grown by low-pressure metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine. Laser diodes fabricated from this structure lased at room temperature. Photoluminescence (PL) measurements were performed from 10 to 230 K. The PL energy increased with temperature from 10 to 70 K and decreased above 70 K. The former was attributed to thermal activation of trapped carriers due to localization in the quantum wells, while the latter was attributed to temperature-induced band-gap shrinkage. The PL intensity as a function of temperature was fitted by employing two nonradiative recombination mechanisms with good agreement, resulting in two activation energies that correspond to losses of photogenerated carriers to nonradiative centers.

High-efficiency LEDs of 1.6–2.4 µm spectral range for medical diagnostics and environment monitoring

High efficient LED structures covering the spectral range of 1.6–2.4 µm have been developed on the basis of GaSb and its solid solutions. The electroluminescent characteristics and their temperature and current dependences have been studied. The radiative and nonradiative recombination mechanisms and their effect on the quantum efficiency have been investigated. A quantum efficiency of 40–60% has been obtained in the quasi-steady mode at room temperature. A short-pulse optical power of 170 mW was reached.

Nonradiative recombination in quantum dots via Coulomb interaction with carriers in the barrier region

A mechanism of nonradiative recombination of nonequilibrium carriers in semiconductor quantum dots (QDs) is suggested and discussed. Recombination of an electron-hole pair localized in a QD occurs via Coulomb (Auger) interaction with carriers in the barrier region. It is shown that the characteristic time of such an Auger process depends on QD parameters, temperature, and carrier density in the barrier region and, under certain conditions, is shorter than the characteristic time of radiative recombination.

Recombination dynamics for photogenerated carriers in germanium-doped ZnSe epilayers grown by molecular beam epitaxy

Germanium-doped ZnSe epilayers have been grown on (001)-oriented semi-insulating GaAs substrates by molecular beam epitaxy. The photoluminescence (PL) spectra exhibit strong near-band edge emission similar to those from undoped, chlorine-doped and gallium-doped samples, though some differences exist. The prominent PL peak at 2.795 eV (10 K) is attributed to the germanium-bound exciton recombination and is accompanied by free exciton (2.802 eV), Ia-type exciton (2.785 eV) and Iv-type exciton (2.775 eV) emission peaks. Following an increase in temperature, the intensity of all the IGe, Ia, and Iv emission peaks decreases gradually, indicating the presence of nonradiative recombination mechanisms with thermal activation energies of 40, 70, and 50 meV respectively. However, for the Iv peak, there is one additional nonradiative recombination mechanism in accordance with the thermally activated transfer of excitons from the Iv-type centers to Ia-type centers. This nonradiative recombination mechanism with activation energy of 9 meV is responsible for the decrease of the Iv peak intensity when the sample temperature is changed from 15 to 100 K. Following an increase in temperature, the Iv peak, Ia peak, and germanium-related peak disappear gradually and successively. Finally, the PL spectrum is dominated by free exciton emission at temperatures exceeding 210 K.

Measurement of the Auger lifetime in GaInAsSb/GaSb heterostructures using the photoacoustic technique

We have studied GaxIn1−xAsySb1−y/GaSb heterostructures for x=0.84 and y=0.14 using the photoacoustic technique with the heat transmission configuration. A theoretical model, which includes all the possible nonradiative recombination mechanisms that contribute to heat generation, was developed to calculate the photoacoustic signal for this type of heterostructure. The Auger recombination lifetime τAuger was determined by fitting our experimental results to the calculated frequency dependence of the theoretical photoacoustic signal. The obtained value for τAuger is compatible with those reported in the literature for semiconductors with band-gap energies below and above 0.5 eV, the energy region where there is a lack of experimental τAuger values.

Light emission from Er at the As-terminated Si(111) surface

Erbium atoms at an arsenic-terminated Si(111) surface can be made to emit light at the 1.55 μm wavelength associated with an internal transition in the Er3+ ion. The As-terminated surface prepared under ultrahigh vacuum conditions has a surface recombination velocity of 50 cm s−1 and partially suppresses competing nonradiative recombination mechanisms. Following the deposition of Er, its characteristic light emission is observed only after oxygen reacts with the surface. The intensity of the light emitted by Er increases significantly upon cooling from 310 to 215 K. No light emission was observed from Er atoms deposited on 7×7 or H-terminated surfaces.

Study of Nonradiative Recombination Mechanisms in Semiconductors by Photoacoustic Measurements

In this work the application of photoacoustic technique (PA) for the study of recombination mechanisms in semiconductor substrates and heterostructures is briefly reviewed. A theoretical model which allows the investigation of nonradiative recombination time and surface recombination velocity was developed. We present the experimental values of such parameters obtained by fitting the theoretical curves to the experimental PA phase data for SiN:H/Si, AlGaAs/GaAs and InGaAsSb/GaSb single heterostructures.

Study of Nonradiative Recombination Mechanisms in Semiconductors by Photoacoustic Measurements

Study of Nonradiative Recombination Mechanisms in Semiconductors by Photoacoustic Measurements

Study of Nonradiative Recombination Mechanisms in Semiconductors by Photoacoustic Measurements

Study of Nonradiative Recombination Mechanisms in Semiconductors by Photoacoustic Measurements

High-power AlGaInAs strained multiquantum welllasers operating at 1.52 µm

1.75 W CW power in AlGaInAs/InP strained QW lasers is demonstrated. Room temperature threshold current densities are 410 A/cm2, and the characteristic temperature is 69 K. The variation in the external differential efficiency with cavity length and temperature reveal the optimum length and show how nonradiative recombination mechanisms limit the performance.

Recombination dynamics in InAsSb quantum-well diode lasers measured using photoluminescence upconversion

We report Shockley–Read–Hall (SRH), radiative, and Auger recombination rates in midinfrared laser structures from time-resolved photoluminescence using frequency upconversion. The devices studied were actual InAsSb/InAlAsSb multiple-quantum-well (MQW) diode lasers emitting near 3.3 μm, which have been previously characterized for laser performance. We extend the initial studies and report on the carrier recombination dynamics. The importance of carrier density motivates a careful examination of carrier density and quantum-well effects. SRH, radiative, and Auger recombination rates (ASRH, Brad, and CAuger, respectively) were measured at 77 K and found to be ASRH−1≈10 ns, Brad≈2×10−10 cm3 s−1, and CAuger⩽1.0×10−29 cm6 s−1, respectively. At 150 K the nonradiative recombination coefficients increased to ASRH−1≈1.7 ns, Brad≈0.78×10−10 cm3 s−1 and CAuger≈7.0×10−28 cm6 s−1, respectively. This study suggests InAsSb/InAlAsSb MQW diode laser performance may be limited by SRH nonradiative recombination mechanisms rather than Auger recombination.

Characterization of high-quality InGaN/GaN multiquantum wells with time-resolved photoluminescence

Recombination in single quantum well and multiquantum well InGaN/GaN structures is studied using time-resolved photoluminescence and pulsed photoluminescence measurements. Room-temperature measurements show a rapid lifetime (0.06 ns) for a single quantum well structure, while an increasingly long decay lifetime is measured for multiquantum wells as more quantum wells are incorporated into the structure. Temperature-dependent lifetime measurements show that a nonradiative recombination mechanism activates above 45 K in the single quantum well but is less important in the multiquantum wells.