Longer Minority Carrier Lifetime Research Articles

Atomic imaging and optical properties of InAs/In0.5Ga0.5As0.5Sb0.5 type II superlattice

High-quality III–V quantum structures, advanced epitaxial technologies, and characterization methods are essential to drive the development of infrared optoelectronic materials and devices. As an important component of type II superlattices, InAs/InxGa1−xAsySb1−y would play an important role in the field of high-performance infrared detectors due to their excellent luminescence efficiency and high crystal quality. However, their interfacial characteristics and the associated minority carrier lifetime are still difficult to identify. In this paper, an atomic imaging technique was used to identify the arrangement and distribution of elements of the InAs/In0.5Ga0.5As0.5Sb0.5 superlattice. Our results confirm the epitaxy mechanism that the quaternary alloy consists of two kinds of ternary alloy in one monolayer. Moreover, by separating the cation and anion columns in the elementally resolved atomic images of the InAs/In0.5Ga0.5As0.5Sb0.5 superlattice, we demonstrate that the interfacial atomic intermixing is less than one molecular layer thickness. Therefore, benefiting from excellent interface quality, InAs/In0.5Ga0.5As0.5Sb0.5 superlattice exhibited high radiation recombination efficiency in the long-wave infrared band (∼8.5 μm), and longer minority carrier lifetime (∼810 ns at 90 K).

Ultrahigh-Quality Ge-on-Glass with a 3.7% Uniaxial Tensile Strain.

While there have been notable advancements in the quality of epitaxial Ge on Si, the crystal quality of bulk Ge remains much superior, which provides an effective method to study the performance potentials of Ge-based semiconductor devices. This study showcases the development of ultrahigh-quality Ge/poly-Si/SiO2 on glass with a Ge thickness reduced to ≤100 nm (10 μm width) through wafer bonding, thinning, and polishing processes. The minority lifetimes measured for the Ge thin films range between 200 and 1000 ns, surpassing those achieved with epi-Ge on Si by at least 20 to 100 times. The wafer bonding process introduces a desirable tensile strain of 0.1%, attributed to thermal expansion mismatch. A Ge microbridge structure was employed to amplify the tensile strain, reaching a maximum uniaxial tensile strain of 3.7%. The much longer minority carrier lifetime together with the strain-induced band gap engineering holds promise for improving light emission efficiency. This work establishes an economical and convenient method for producing high-quality tensile-strained Ge thin films, a pivotal step in exploring the potential of Ge in light emission applications.

Relationship between epi-wafer photoluminescence and focal plane array performances of InGaAs detectors

The relationship between photoluminescence properties of InGaAs detector epi-wafers and the performances of focal plane arrays has been established according to the measurements of various samples. The average signal, dark signal and noise of the fabricated focal plane arrays were characterized and correlated to the photoluminescence intensities and nonuniformities of the epi-wafers. The average response signal is increased as the increased photoluminescence. The signal nonuniformity and dark signal are markedly related to nonuniformity of photoluminescence intensity, while the noise voltages are not correlated to photoluminescence results. The microwave photoconductance decay measurements reveal that the epi-wafers with stronger photoluminescence intensity has longer minority carrier lifetime. This work supplies a feasible pathway to evaluate and predict the performances of focal plane arrays fabricated by InGaAs detector epi-wafers before device processing.

Pulsed-laser-deposited lead sulfide nanoparticles based decoration of porous silicon layer as an effective passivation treatment for multicrystalline silicon

We report on the use of pulsed laser deposition (PLD) of PbS nanoparticles (PbS-NPs) on porous silicon layers in order to passivate multicrystalline silicon (mc-Si) substrates intended for solar cells applications. The porous silicon (PS) layer was first obtained through the electrochemical anodization of the mc-Si substrate, and then the PLD technique was used to decorate the PS layer by PbS-NPs at room temperature. By varying the number of laser ablation pulses (NLP) from 50 to 1200, the average size of the PbS-NPs was varied from ~2 nm to ~10 nm. The X-ray diffraction analysis has confirmed the crystalline quality of the PbS-NPs, whereas the transmission electron microscopy observations showed the uniform decoration of the PS by the PbS-NPs. By combining different characterization techniques, we were able to identify NLP = 200 as the optimal decoration condition that leads to the best passivation, in terms of the lowest surface reflectivity (of 15% at 500 nm wavelength), the highest PL intensity of the PS layer (centered around 633 nm) and the longest minority carrier lifetime (as long as ~430 µs versus 40 µs for the bare treated PS layer and 2.2 µs for the untreated bare mc-Si).

High open‐circuit voltage CuSbS2 solar cells achieved through the formation of epitaxial growth of CdS/CuSbS2 hetero‐interface by post‐annealing treatment

AbstractThe earth‐abundant and environmentally‐friendly CuSbS2 solar cells have been struggling with low device performance, especially poor open circuit voltage (Voc). In this work, post‐annealing treatment of the CuSbS2/CdS heterojunction performed on CuSbS2‐based solar cells was firstly reported. With this treatment, we demonstrated CuSbS2 solar cells with a record Voc of 622 mV. The improvement of device performance was found peaked at 250°C post‐annealing which mainly benefits from the significantly boosted open‐circuit voltage and short‐circuit current. The study of microstructure by high‐resolution transmission electron microscopy revealed that such improvement could be attributed to the formation of epitaxial CuSbS2/CdS hetero‐interface upon heat treatment, which reduces the interface defect density that may lead to reduced Voc deficit. Besides, results of photoluminescence and time‐resolved photoluminescence measurements also indicated improved electrical properties of completed devices with higher photoluminescence intensity and longer minority carrier lifetime.

Optimization of the defects and the nonradiative lifetime of GaAs/AlGaAs double heterostructures

We used Raman scattering and time-resolved photoluminescence spectroscopy to investigate the molecular-beam-epitaxy (MBE) growth parameters that optimize the structural defects and therefore the internal radiative quantum efficiency of MBE-grown GaAs/AlGaAs double heterostructures (DH). The DH structures were grown at two different temperatures and three different As/Ga flux ratios to determine the conditions for an optimized structure with the longest nonradiative minority carrier lifetime. Raman scattering measurements show an improvement in the lattice disorder in the AlGaAs and GaAs layers as the As/Ga flux ratio is reduced from 40 to 15 and as the growth temperature is increased from 550 to 595 °C. The optimized structure is obtained with the As/Ga flux ratio equal to 15 and the substrate temperature 595 °C. This is consistent with the fact that the optimized structure has the longest minority carrier lifetime. Moreover, our Raman studies reveal that incorporation of a distributed Bragg reflector layer between the substrate and DH structures significantly reduces the defect density in the subsequent epitaxial layers.

Low dose 60Co gamma-irradiation effects on electronic carrier transport and DC characteristics of AlGaN/GaN high-electron-mobility transistors

ABSTRACTThe impact of internal irradiation with secondary Compton electrons, generated by gamma-photons, on the characteristics of III-N/GaN-based devices was explored. N-channel AlGaN/GaN high-electron-mobility transistors (HEMTs) were exposed to gamma-radiation from a 60Co source for doses up to 600 Gy. Temperature-dependent electron beam-induced current (EBIC) was employed to measure minority carrier transport properties. For low doses below ∼250 Gy, the minority carrier diffusion length in AlGaN/GaN HEMTs is shown to increase by about 40%. This increase is likely due to longer minority carrier lifetime induced by internal Compton electron irradiation. An associated decrease in activation energy, extracted from temperature-dependent EBIC, was also found. The obtained increase in transconductance and decrease in gate leakage current indicate an improvement in performance of the devices after low doses of irradiation. For high doses of gamma-irradiation, above ∼300 Gy, the performance of HEMTs showed a deterioration. The deterioration results from the onset of increased carrier scattering due to additional radiation-induced defects, as is translated in a decrease of minority carrier diffusion length.

Impact of Sb Incorporation on MOVPE-Grown “Bulk” InGaAs(Sb)N Films for Solar Cell Application

We have investigated the impacts of Sb incorporation on the microstructural, optical, electrical, and carrier dynamics properties of bulk InGaAsSbN films in a comparative study of InGaAsN and InGaAsSbN materials grown by metal–organic vapor phase epitaxy (MOVPE). These films were grown at the relatively high temperature of 600 °C and annealed at 800 °C for 30 min. Transmission electron microscopy studies indicate compositional and structural homogeneity of the InGaAsN and InGaAsSbN films. Low-temperature time-resolved photoluminescence measurements of the MOVPE-grown InGaAsN film show a longer minority carrier lifetime (∼40 ns) than observed for the InGaAsSbN film (∼26 – 27 ns). In addition, single-junction solar cells with an InGaAsN (InGaAsSbN) base layer exhibit an open-circuit voltage of 0.64 (0.58) V, a short-circuit current of 17.13 (16.89) mA/cm2, a fill factor (FF) of 77.55 (74.29)%, and an efficiency of 8.57 (7.31)%. Sb incorporation in InGaAsN adversely affects solar cell performance due to a reduced minority carrier lifetime correlated with the formation of defects and narrow depletion region width resulting from a higher background carbon impurity level.

Effect of Sn/Zn/Cu precursor stack thickness on two-step processed kesterite solar cells

We have fabricated Cu2ZnSnSe4 (CZTSe) solar cells with different absorber layer thickness. Absorber layers with different thicknesses were fabricated by changing the thickness of e-beam evaporated Sn/Zn/Cu precursor stacks and then selenization in a rapid thermal processing system. Scanning electron microscopy revealed that by increasing the thickness the morphology of CZTSe films improves substantially and energy dispersive spectrometry measurements showed that the Cu to Sn ratio increased with increasing the film thickness, despite a similar Cu to Sn ratio in the starting layers. A longer minority carrier lifetime and higher open circuit voltage were achieved for solar cells with thicker absorber layers. A maximum conversion efficiency of 7.8% (without anti reflection coating) was achieved for a solar cell with 1.7μm thickness in which a low doping density of the order of 1015cm−3 was measured, leading to a wide space charge region of about 300nm.

Optical absorption and intrinsic recombination in relaxed and strained InAs1–xSbx alloys for mid-wavelength infrared application

The intrinsic carrier recombination lifetime in relaxed and strained InAs1−xSbx alloys is investigated using the full-band Green's function theory. By computing the phonon-perturbed electron self-energy of the system, both direct and phonon-assisted indirect Auger and radiative processes are studied as functions of antimony molar fractions, lattice temperatures and applied in-plane biaxial strains. To improve the overall accuracy of the calculation, an empirical pseudopotential band structure for the alloy is also fitted to the measured band extrema and effective masses under different biaxial strains. A set of effective screened potentials valid for all the needed antimony fractions x and biaxial strains ϵ, therefore, is obtained and applied to the calculation. The results showed reduced total Auger recombination rates and enhanced radiative recombination rates in InAsSb alloys at room temperature when a compressive strain is applied. Furthermore, the study on the widely employed mid-wavelength infrared detector material, InAs0.91Sb0.09, strained by an InAs substrate, demonstrated that much longer minority carrier lifetime can be achieved compared to that in the lattice-matched situation when the lattice temperature is above 200 K.

Plasma-etching fabrication and properties of black silicon by using sputtered silver nanoparticles as micromasks

A nanohill structure has been fabricated on a silicon surface via a micromask formed by a radio-frequency magnetron sputtering deposition of silver nanoparticles and a following dry etching under SF6 plasma. The proposed technique does not rely on oxygen gas to eliminate the damages from oxygen plasma and to increase the lifetime of the silicon crystal. The experiments indicate that the morphology and particle size distribution of silver nanoparticles determine the reflectivity of the textured silicon wafer. Interestingly, the nanohill structure exhibits a stronger light confinement ability than the columnar one, leading to a lower reflectivity. A longer minority carrier lifetime is obtained in such nanohill structures with a lower defect concentration on the surface. This work provides a pathway to fabricating black silicon of excellent light confinement structure, which may have potential for applications in some localized surface plasmons-relevant areas.

Improvement on the Electrical Characteristics of HfO[sub x]N[sub y]-Gated Metal-Oxide-Semiconductor Devices by High-Temperature Annealing

The electrical characteristics of HfO x N y -gated metal-oxide-semiconductor devices are significantly affected by the amount of defects in Si substrate. Devices with a low defect region near the Si surface were formed in this work using high-temperature annealing in a hydrogen ambient. Experimental results show longer minority carrier lifetime in silicon substrate, lower gate leakage current, and reduced interface trap density (D it ), which are attributable to the decrease in the interstitial oxygen (O i ) and crystal-originated-particle defects as well as better surface quality at HfO x N y /Si interface.

Supergain transistors on high-purity float-zone silicon substrate

Since float-zone (FZ) silicon has lower contamination and longer minority carrier lifetime than those in Czochralski silicon and other semiconductor materials, it has potential advantages to fabricate a bipolar junction transistor on the FZ substrate to achieve high gain at very low current levels. In this report, the authors present preliminary experimental results on supergain bipolar junction transistors fabricated on unusual FZ refined high-resistivity silicon substrate and by ion implantation technology. A phosphorus-doped polycrystalline silicon backside gettering layer has been employed to preserve the long carrier lifetime of the high-purity FZ silicon. Bipolar junction transistors have demonstrated high current gain, more than 3300 for ultralow base current levels of 10 pA in this study. Possible applications of high-purity FZ silicon on some advanced semiconductor devices and circuits are discussed in this letter.

High-gain bipolar detector on float-zone silicon

Since the float-zone (FZ) silicon has lower contaminations and longer minority-carrier lifetime than those in Czochralski silicon and other semiconductor materials, it has potential advantages to fabricate bipolar detectors on the high-purity FZ silicon substrate to achieve a high gain at ultra-low-signal levels. The authors present preliminary experimental results on a bipolar detector fabricated on an unusual high-purity FZ silicon substrate. A backside gettering layer of phosphorus-doped polysilicon was employed to preserve the long carrier lifetime of the high-purity FZ silicon. The device has been investigated in the detection of a continuous flux of X-ray and infrared light. The bipolar detector with a circular emitter of 2 mm diameter has demonstrated high gains up to 3820 for 22 keV X-ray from a 1 mCi Cd radioactive source (the X-ray photon flux, received by the detector is estimated to be ∼7.77×10 4/s). High gain up to 4400 for 0.17 nW light with a wavelength of 0.83 μm has been observed for the same device.

Impurity investigation and structural quality determination of GaAs epilayers from mixed solvents (Ga+Bi)

GaAs epilayers grown from 100% Ga, 100% Bi and mixed solvents were investigated by low-temperature photoluminescence (PL) and Auger electron spectroscopy (AES). The change in the photoluminescence spectra was analyzed as a function of the bismuth content in the solution. From the AES, the carbon (C) concentration in 50% Bi-grown layers is less when compared to other Bi-grown layer and Ga-grown layer. There is no Bi related peak in the GaAs epilayers which is grown using Bi mixed solvents. The structural quality of the epilayer due to the variation of Bi in Ga solvent was revealed by molten KOH. The etch pit density (EPD) reduced to more than half the order of magnitude for the epilayer grown from the Bi solvent when compared to Ga-grown epilayer. The carrier lifetime was determined by the time-resolved photoluminescence (TRP). Epilayer from Bi 50% solvent has longer minority carrier lifetime.

Gain coefficient, quantum efficiency, transparency current density, and internal loss of the AlGaAs-GaAs-based lasers on Si substrate

The AlGaAs-GaAs based lasers on Si substrate with GaAs quantum-well and island-like active regions are fabricated by metal-organic chemical vapor deposition. The parameters of internal quantum efficiency, gain coefficient, transparency current density, and the internal loss that describe the operating characteristics of laser diodes are investigated. The optical confinement factor is calculated with the assumption that the light emission occurs from the island regions only. In addition, longer minority carrier lifetime obtained for the lasers with island-like active regions reveals their improved characteristics over conventional quantum-well lasers.

Transient response of gallium arsenide and silicon solar cells under laser pulse

Solar cells can be used as receivers in laser power beaming applications [1]. Power beamed to a photovoltaic array could power a satellite, an orbital transfer vehicle or a lunar base. Understanding solar cell response to the pulsed output of a free-electron laser (FEL) is important for evaluation of power-beaming applications. In this work we investigate the time response of gallium arsenide and silicon solar cells to a 25 ns monochromatic pulse input. The PC-1D computer code is used to analyze the cell current during and after the pulse for various conditions. For GaAs cells, current decay was studied at 511, 840 and 870 nm. Most of the results have been calculated for a peak intensity of 50 W cm −2, which corresponds to roughly 500 suns peak concentration. Silicon cells have a longer minority carrier lifetime and weaker optical absorption, resulting in longer characteristic time constants. Si cell performance was studied at 900, 950 and 1060 nm wavelengths.

Time-resolved photoluminescence characterization of GaAs and AlGaAs on Si substrate grown by MOCVD

Abstract GaAs layers and AlGaAs solar cells grown on Si substrates have been characterized by time-resolved photoluminescence (TRP). The effects of the growth temperature, the strained layer superlattice (SLS), and the thermal cycle annealing (TCA) on the TRP characteristics are discussed. The minority carrier lifetime is increased with increasing growth temperature and by using SLS + TCA. The longest minority carrier lifetime of GaAs on Si obtained in this study is 0.50 ns.

Aspects of “High Minority-Carrier Lifetime” GaAs on Si Using A Novel SiGe/Ge Buffer

Heteroepitaxial GaAs-on-Si utilizing a Si 0.4 Ge 0.96 /Ge buffer, with a hole minority-carrier lifetime as long as ∼ 2.5 nsec is described. This is the longest minority-carrier lifetime in GaAs grown on Si reported to date by any approach. Here we discuss the microstructural aspects of this heteroepitaxial system, including a crossectional transmission electron microscopy (XTEM) study of the interface of the SiGe/Ge buffer and the role of the SiGe layer. An x-ray double crystal diffraction (DCD) study of the GaAs layers is also presented. The SiGe/Ge buffer approach to heteroepitaxial GaAs on Si is a result of two observations: (1) SiGe epitaxial layers grown on Ge are under biaxial compressive stress (from DCD) and (2) dislocations tend to bend over into the Ge substrate (from TEM). These data and a description of the heteroepitaxy of SiGe layers on Ge are presented.