Lifetime Of Nonequilibrium Charge Carriers Research Articles

Relationships Between Strain and Recombination in Intermediate Growth Stages of GaN

Using metalorganic chemical vapor deposition, we heteroepitaxially grew undoped gallium nitride epilayers on sapphire. Assessing the epilayers at different growth stages, we investigated changes in epilayer strain and the lifetime of minority nonequilibrium charge carriers. The in-plane compressive strain was evaluated by x-ray diffraction and bandgap photoluminescence. The epilayer thickness ranged from 200 nm (islets) to 3.5 μm (continuous structure). The carrier lifetimes, measured using a light-induced transient grating technique, revealed a correlation between strain and the density of edge-type threading dislocations. This dislocation density was 109 cm−2 to 1011 cm−2, corresponding to the dominant mechanism for nonradiative carrier recombination. How the carrier lifetime depended on the growth stage differed between the surface and interfacial measurements. On the surface side, the carrier lifetime increased monotonically up to ~500 ps with thickness; on the interface side, the lifetime changed little with thickness, except in the thickest sample, where the carrier lifetime increased with thickness. We attributed this behavior to defect healing aided by long-term annealing, leading to mutual lateral motion and annihilation of mixed threading dislocations.

Doslidzhennya rekombinatsiynykh kharakterystyk Cz-kremniyu, implantovanoho ionamy zaliza

A comparative study of the defect formation and changes in the lifetime of nonequilibrium minority charge carriers in silicon while gettering the iron impurity with the use of a combined getter “porous silicon layer + aluminum film” is carried out. It is shown that, while annealing specimens with no getter layer, iron silicide and defects of the vacancy type are formed in the implanted regions and, as a result, a considerable reduction in the lifetime of nonequilibrium minority charge carriers is observed. The influence of the getter layer on the defect formation and the redistribution of iron atoms implanted into silicon are studied in the case of high iron concentrations in a vicinity of the surface. The presence of a getter layer is shown to reduce the efficiency of the silicide formation in the implanted region and to increase the concentration of interstitial defects in silicon. A model of the gettering process is proposed, which makes allowance for the gettering-induced reduction of the iron atom concentration in the implanted region and a decrease of the vacancy defect concentration, as well as the simultaneous increase of the concentration of interstitial-type defects associated with the formation of complexes of iron and boron atoms. These complexes are recombination-active and do not allow the lifetime of charge carriers to be restored to the initial value.

Effect of annealing on the nonequilibrium carrier lifetime in GaAs grown at low temperatures

GaAs samples grown by molecular-beam epitaxy at low (230°C) temperatures are investigated. One of the samples is subjected to aftergrowth annealing at 600°C. Using an unconventional pump-probe scheme for measuring the dynamic variation in the light refractive index, the nonequilibrium charge-carrier lifetime (275 ± 30 fs before annealing) is determined. Such a short carrier lifetime in the unannealed material is due to the high concentration of point defects, mainly AsGa antisite defects. According to X-ray diffraction and steady-state optical absorption data, the AsGa concentration in the samples is 3 × 1019 cm−3, which corresponds to an arsenic excess of 0.26 at %. Upon annealing at 600°C, the superstoichiometric As defects self-organize and form As nanoinclusions in the GaAs crystal matrix. It is shown that in this case the nonequilibrium charge-carrier lifetime increases to 452 ± 5 fs. This lifetime is apparently ensured by the capture of non-equilibrium charge carriers at metal As nanoinclusions.

Production of high-purity Cd, Zn, and Te by multistage vacuum distillation

The quality of detector single crystals is determined by the lifetime and mobility of nonequilibrium charge carriers, which depend on the purity of the components used for synthesis. An original setup for multistage vacuum distillation of Cd, Zn, and Te is designed, which is characterized by the simplicity of equipment and the minimal loss of the initial material. The purified materials have low contents of oxygen and metal impurities, which allow one to significantly increase the purity of the synthesized crystals.

Getter formation in silicon by implantation of antimony ions

A porous silicon layer as a getter of uncontrolled impurities has been prepared by implantation of Sb+ into silicon and subsequent thermal treatments. The lifetime of nonequilibrium charge carriers in n- and p-type silicon wafers with a getter layer is 3–4 times longer than that without a getter.

Effect of the microstructure on electrical properties of high-purity germanium

The interrelation between the electrical properties and the microstructure of high-purity germanium crystals has been revealed. The electrical conductivity of polycrystalline samples increases and the life-time of nonequilibrium charge carriers in them decreases with a decrease in the crystallite sizes.

Nonequilibrium Charge Carrier Lifetime Testing Equipment for Semiconductor Materials by a Contactless Microwave Phase Method

The accurate measurement of nonequilibrium charge carrier lifetime is of vital significance in research and manufacture of crystalline silicon solar cells. A testing equipment based on a contactless microwave phase method was implemented by being embedded with GPIB, FPGA and a lock-in analyzer. A friendly operation interface was developed, based on the graphic programming language LabVIEW. The virtue of the equipment is achieved by automatic data acquisition and processing, which improves the automatization, efficiency and accuracy of the measurement.

GaAs Pixel Detectors

ABSTRACTResults of investigation of X-ray sensors on the basis of GaAs compensated with chromium (HR GaAs) are presented in this work. HR GaAs material is shown to have the following physical parameters: the resistivity about 1GOhm*cm, the nonequilibrium charge carrier lifetime – hundreds of nanoseconds. Prototypes of microstrip and array HR GaAs sensors have been manufactured and tested. It is demonstrated that the sensors provide spatial resolution according to the pixel pitch and allow obtaining high quality X-ray images.

Dipole antennas based on SI-GaAs:Cr for generation and detection of terahertz radiation

Design and technology of fabrication of dipole terahertz radiation emitters and detectors based on semiinsulating GaAs compensated with chromium and having the nonequilibrium charge carrier lifetime of the order of 100 ns are described. Generation and detection of subterahertz radiation in dipole antennas excited by femtosecond laser pulses are experimentally investigated depending on the topology of contact electrodes and the parameters of the active medium.

Increases of the non-equilibrium charge carrier lifetime in silicon crystals

The article describes possibility increase of the non-equilibrium charge carrier lifetime in silicon monocrystals at use of initial raw materials with the increased content of impurity is considered

Experimental evaluation of the carrier lifetime in GaAs grown at low temperature

The relaxation dynamics of nonequilibrium charge carriers in gallium arsenide epitaxial films grown by molecular-beam epitaxy at low temperatures has been studied. The growth conditions of the epitaxial layer provided an excess arsenic content of 1.2% in the layer. In a material of this kind, the carrier lifetime is <1 ps. To examine carrier relaxation in the femtosecond range, an original scheme for measuring the refractive index dynamics was developed on the basis of the pump-probe technique. The lifetime of nonequilibrium charge carriers was evaluated to be (200 ± 35) fs.

Estimation of the ultimate efficiency of a three-pin solar cell based on the GaAs/Si heterostructure

The ultimate efficiency of a three-pin solar cell based on the GaAs/Si structure is calculated by means of numerical simulation in a diffusion-drift approximation. Dependences of the efficiency on the GaAs layer thickness and the density of dislocations threading in this layer, which are known to affect the lifetime of nonequilibrium charge carriers. It is shown that the maximum limit efficiency (27%) of such a structure is reached at the GaAs layer thickness of about 1.4 µm and the density of threading dislocations of less than 106 cm−2.

A high-temperature radiation-resistant rectifier based on p+-n junctions in 4H-SiC ion-implanted with aluminum

A combination of a high-dose (5 s- 1016 cm-2) implantation of Al ions into epitaxial n-type 4H SiC layers grown by chemical deposition from th e vapor phase and rapid (15 s) thermal annealing at 1700–1750°C has been used to form layers with a rectangular impurity profile according to the mechanism of solid-phase epitaxial crystallization. The combined effects of enhanced diffusion of radiation defects after implantation and gettering of defects during annealing bring about an improvement in the quality of the initial material, which ensures an increase in the diffusion length of the minority charge carriers by several times. Metastable states annealed within different temperature ranges are formed in SiC under the effect of irradiation with various particles. Low-temperature annealing of radiation defects increases the radiation and temporal lifetime of devices under irradiation. High-temperature annealing of radiation defects makes it possible to vary the lifetime of nonequilibrium charge carriers, i.e, vary the frequency range of devices. The radiation resistance of SiC-based devices increases as the operation temperature is increased to 500°C.

Effect of electron irradiation attenuated by aluminum screens on the electrical parameters of p-n silicon structures

We have studied the influence of irradiation by 6-MeV electrons via flat aluminum screens with thicknesses d = 2−14 mm (mass thicknesses, 0.5–3.8 g/cm2) on the properties of p +-n-n + silicon structures, including the nonequilibrium charge carrier lifetime (τ), reverse current (I R), and forward current-voltage (I-U) characteristics. In the case of a screen with d = 14 mm (3.8 g/cm2), the irradiated structures exhibit significantly smaller changes in I R values and I-U curves compared to those for d = 2–12 mm, whereas a decrease in τ (from 20 to 1.5 μs) is the same.

10.1007/s11453-008-2020-y

The rates of radiative recombination (including transitions induced by enhanced luminescence) and nonradiative recombination, internal quantum yield of luminescence, and the matrix element for band-to-band optical transitions were determined for the first time for InAsSb/InAsSbP diode lasers oscillating at wavelengths of 3.1–3.2 μm. It is established that the contribution of nonradiative recombination to the lasing threshold can be as large as 97%. The internal quantum yield of luminescence for the InAs0.97Sb0.03 compound is no higher than 3%. Most likely, the nonradiative channel is formed with involvement of Auger recombination with the constant C = 4.2 × 10−38 m6s−1 (T = 77 K). The studied samples of lasers feature relatively low optical losses ρ = 900 m−1 and internal quantum efficiency of emission at the level of 0.6. The spontaneous lifetime of nonequilibrium charge carriers as determined from the radiative-recombination rate is equal to 6 × 10−8 s, which is consistent with known published data.

Lifetime of nonequilibrium charge carriers in the base of p-n-junction semiconductor diode at arbitrary injection levels

In the approximation of exponential distribution of nonequilibrium charge carriers in the base of semiconductor p-n-junction diode a formula is obtained for lifetime calculation, which is valid at arbitrary injection levels. The lifetime is determined via measurements of only stationary characteristics of diodes (dc-CVC and low-frequency differential resistance). These characteristics, as well as the dependence of the barrier capacity on the reverse voltage, for determination of equilibrium concentration of carriers in the diode base, have been measured for D226B alloy diodes. The dependence of the lifetime of nonequilibrium carriers on the injection level, calculated from experimental data, agrees with the Shockley-Read theory of recombination; this agreement may be considered as a justification of assumptions made for lifetime calculation.

Optical parameters of diode lasers based on an InAsSb/InAsSbP heterostructure

The rates of radiative recombination (including transitions induced by enhanced luminescence) and nonradiative recombination, internal quantum yield of luminescence, and the matrix element for band-to-band optical transitions were determined for the first time for InAsSb/InAsSbP diode lasers oscillating at wavelengths of 3.1–3.2 μm. It is established that the contribution of nonradiative recombination to the lasing threshold can be as large as 97%. The internal quantum yield of luminescence for the InAs0.97Sb0.03 compound is no higher than 3%. Most likely, the nonradiative channel is formed with involvement of Auger recombination with the constant C = 4.2 × 10−38 m6s−1 (T = 77 K). The studied samples of lasers feature relatively low optical losses ρ = 900 m−1 and internal quantum efficiency of emission at the level of 0.6. The spontaneous lifetime of nonequilibrium charge carriers as determined from the radiative-recombination rate is equal to 6 × 10−8 s, which is consistent with known published data.

Mechanisms of recombination of nonequilibrium charge carriers in epitaxial CdxHg1−x Te (x = 0.20–0.23) layers

The experimental temperature dependences of the photosensitivity and the data on the lifetime of nonequilibrium charge carriers in epitaxial CdxHg1−x Te layers with x = 0.20–0.23 were used to show that, in the region of intrinsic and extrinsic conductivity in n-type films grown by molecular beam epitaxy, CHCC Auger recombination is the prevailing recombination mechanism. At the same time, in p-type films grown by liquid-or vapor-phase epitaxy, it is observed that, in the region of extrinsic conductivity, CHLH Auger recombination competes with Shockley-Read recombination. The n-type films grown by molecular beam epitaxy contain a much lower concentration of recombination centers than the p-type films grown by liquid-or gasphase epitaxy.

High-temperature annealing of electron-irradiated high-voltage diode structures on neutron transmutation-doped Si

High-voltage diode structures were fabricated in high-resistance neutron transmutation-doped (NTD) silicon and irradiated with 6 MeV electrons. A non-equilibrium minority charge carrier (NMCC) lifetime was measured in the high-resistance region of p +–n structures and deep-level transient spectroscopy (DLTS) was used to determine the concentration and energy level positions of radiation-induced defects as a function of annealing temperature in the range 300--800 °C. The results suggest that in structures of the type investigated here, defects are formed with high thermal stability up to 800 °C and with a high formation efficiency when exposed to radiation. These defects’ properties as recombination centers can be used for the fabrication of fast power diodes; their incorporation into device structures should be made at the fabrication stage preceding the formation of ohmic contacts.

Silicon Passivated by Insulating Erbium Oxide Films

The recombination properties of silicon passivated by insulating films of erbium oxide (Er2O3) have been studied. After deposition of an oxide film, the effective lifetime of nonequilibrium charge carriers, measured by method of nonstationary photoconductivity relaxation, increased by a factor of two to three as compared to the initial value. The rates of the surface recombination of charge carriers at the silicon-oxide interface have been determined. The insulating films of erbium oxide are promising passivating coatings for siliconbased devices and integrations.