Competition of N-passivation and Te-passivation in hydrogenation of Te-doped (Ga,In)(N,As)

(Ga,In)(N,As) lattice matched to GaAs with a band gap of 1 eV is employed as active material in high-efficiency III–V solar cells. Te-doped Ga_0.934In_0.066N_0.023As_0.977 layers were grown by metal-organic vapor-phase epitaxy on (1 0 0) GaAs. The samples were highly doped n-type with carrier concentrations ranging from about 10¹⁷–10¹⁹ cm⁻³. Pieces of the samples were hydrogenated with H-doses of 10¹⁸ ion/cm². The optical and electrical properties of the samples before and after hydrogenation were studied by low-temperature photoluminescence and magnetotransport. In undoped samples hydrogen is known to form N–H complexes which strongly reduce the local perturbation of the lattice due to nitrogen and thus reverse the N-induced global changes of the band structure. Combined analysis of photoluminescence and transport measurements on Te-doped samples, however, indicates a competition between N–H formation and passivation of the Te donor favoring the latter. Hardly any band structure changes due to hydrogenation are observed in these Te-doped samples, instead a strong reduction of the free-carrier concentration is observed after hydrogenation.     

Electrophysical properties of heat-treated gallium arsenide

The electrical conductivity, Hall effect, ionization energy, and defect concentration of GaAs samples subjected to various forms of heat treatment were studied. The original material comprised single crystals grown by the Bridgman and Czochralski methods with electron concentrations of 2·10¹⁵–7·10¹⁷ cm^–3. The ionization energy and defect concentration were calculated with an electronic computer. The thermal conversion of GaAs was attributed to traces of copper, lattice defects, and residual impurities. The mobility varied in a complicated manner with the temperature of heat treatment in GaAs samples retaining their original n-type conductivity.Translated from Izvestiya VU Z, Fizika, No. 3, pp. 69–76, March, 1973.     

Growth and characterization of DyP/GaAs and DyAs/GaAs-based heterostructures and superlattices

Details of the structural and electrical properties of epitaxial DyP/GaAs and DyAs/GaAs is reported. DyP is lattice matched to GaAs, with a room temperature mismatch of less than 0.01%. DyAs, on the other hand, has a mismatch of nearly 2.4%. Both DyP and DyAs have been grown by solid source MBE using custom designed group V thermal cracker cells and group III high-temperature effusion cells. High-quality DyP and DyAs epilayers, as determined by XRD, TEM, and AFM analysis, were obtained for growth temperatures ranging from 500°C to 600°C with growth rates between 0.5 and 0.7 μm/h. The DyP epilayers are n-type with measured electron concentrations of the order of 3×10²⁰ to 4×10²⁰ cm⁻³, with room temperature mobilities of 250–300 cm²/V s, and with a barrier height of 0.75 eV to GaAs. The DyAs epilayers are also n-type with concentration of 1×10²¹ to 2×10²¹ cm⁻³, with mobilities between 25 and 40 cm²/V s. DyP is stable in air with no apparent oxidation taking place, even after months of ambient exposure to untreated air.     

Optimization of carbon incorporation in GaAs during molecular beam epitaxial growth

Carbon-doped GaAs with dopant concentrations up to about 10²⁰ cm^–3 has been grown by molecular beam epitaxy. Above a critical carbon concentration, which depends on the deposition parameters, the surface deteriorates and loses its mirror-like appearance. From X-ray diffractometry and scanning electron microscopy, a diagram is established separating two areas with rough and mirror-like surface morphologies. The electrical properties as well as the morphology of GaAs : C can be simultaneously improved by a careful adjustment of the deposition parameters according to this diagram. On leave at: Tokyo Institute of Technology, Research Center for Quantum Effect Electronics, 2-12-1 O-okayama, Meguro-ku, Tokyo 152, Japan     

Far infrared surface electromagnetic waves propagation on A3B5 semiconductors

The real and imaginary parts of surface electromagnetic waves (SEW) refraction index n_ef in n-type InSb, GaAs and InP have been measured in FIR region (=85–142 cm^–1). The n_ef measurements allowed to determine plasma frequency _p and plasmon damping . The obtained nonlinear SEW propagation distance L dependence on Te impurity concentration in GaAs (N=10¹⁷–10¹⁹ cm^–3) was explained taking into account the conduction band nonparabolity as well as the presence of isostructural phase transition at N=2×10¹⁰ cm^–3.     

Formation of p-type layer by KrF excimer laser doping of carbon into GaAs in CH4 gas ambient

Carbon doping of GaAs using a KrF excimer laser to form a p-type active layer is described. Methane gas (CH₄) was used as a source of the C acceptor. Various quantities such as sheet resistance, surface carrier density, Hall mobility, and depth profile of C-doped GaAs are measured as the functions of laser fluence and laser pulse. It is shown that C atoms are doped only within a limited depth as shallow as 50 nm or less and with extremely high concentration exceeding 1×10²¹ cm^–3. The maximum activation efficiency is found to be 69.0%. Laser induced changes of surface morphologies and electron diffraction patterns are also discussed. Furthermore, non-alloyed ohmic contacts using laser-doped p-type GaAs are demonstrated.     

Growth kinetics of Si-molecular beam epitaxy

Growth mode, surface morphology, crystal perfection and growth rate of siliconmolecular beam epitaxy films were observed as function of temperature (450°–950°C), silicon flux density (8×10¹⁴–8×10¹⁵cm²/s) and surface orientation (111, 110, 100). Within the varied parameters growth proceeds by the two-dimensional growth mode via the lateral motion of atomic steps originating from the slight misorientation of commercially available substrates (typically 0.25°). Single crystalline films with high lattice perfection and smooth surfaces result from this growth mode. The growth rate — linearly dependent on Si-flux density and independant of temperature and orientation — indicates a condensation coefficient near unity. An atomic step flow model on the basis of the Burton-Cabrera-Frank theory explains this behaviour by mobile adatoms with low activation energy of diffusion.     

Generation mechanism and thermal stability of high carrier concentrations by KrF-excimer-laser doping of Si into GaAs

The generation mechanism and thermal stability of high carrier concentrations in GaAs formed by KrF-excimer-laser doping with Si using SiH₄ gas are investigated. The channeling Particle-Induced X-ray Emission (PIXE) analysis reveals that a high substitutional fraction of over 90% and preferential replacement of Si atoms on Ga sites result in the generation of carrier concentrations as high as 5×10¹⁹ cm^–3. In addition, the thermal stability of the doped regions is studied. The high carrier concentrations in a nonthermal equilibrium state return to a thermal equilibrium state by postannealing.Presented at LASERION'93, Munich, June 21–23, 1993     

Effect of electron irradiation on the properties of germanium-doped gallium arsenide

The Hall effect, electrical conductivity (77–370 K), and photoluminescence spectra (77 K) are studied in single-crystals of nuclearly doped GaAs (NDG) and GaAs doped with Ge by the metallurgical method after irradiation by electrons (E= 1 MeV, D=1.1·10¹⁵–3.8·10¹⁸ cm^–2). Initial electron concentrations were n= 1.7·10¹⁷ cm^–3 and n₀=2.6·10¹⁷ cm^–3 respectively. In the GaAs doped during crystal growth by the Czochralski method the degree of compensation related to the amphoteric impurity Ge is higher (K=0.8) than in the NDG (K=0.4) for identical initial electron concentration. It was established that the rate of charge carrier removal in GaAs is lower than in NDG, while radiation defects are more thermostable in NDG. The energy spectrum of radiation defects and radiating recombination centers, and the basic steps in reestablishment of electrophysical and optical properties in GaAs and NDG are similar, i.e., they do not depend on the method of germanium doping.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 82–86, April, 1991.     

Spectral Properties of Single Crystals of Synthetic Diamond

The half-width of the spectrum of Raman scattering (RS) of the first order of a diamond single crystal grown in a nickel-free system containing nitrogen getters is identical to all growth sectors (1.69 ± 0.02 cm^–1). The sectorial inhomogeneity is not reflected in the transmission spectra and birefringence of this crystal. The nitrogen concentration is 4·10¹⁷ cm^–3. For different growth sectors of the diamond crystal grown in the Ni–Fe–C system, the half-width of the Raman line varies from 1.74 to 2.08 cm^–1, differences in the transmission spectra and birefringence are observed, and photoluminescence is revealed. The concentration of nitrogen in the growth sectors {001} is 1.6·10¹⁹ cm^–3, the content of nickel is estimated to be at a level of 10¹⁹ cm^–3, and the content of nitrogen in the {¯111} sectors is 4·10¹⁹ cm^–3.     

Studies on excimer laser doping of GaAs using sulphur adsorbate as dopant source

Excimer laser doping of GaAs using sulphur adsorbate as a dopant source is demonstrated. Box-like n-type layers of depths of about 100 nm with carrier concentration as high as (23)×10¹⁹ cm^–3 are formed. Passivation of GaAs using a (NH₄)₂S_x solution for 40 min followed by sublimation of the excess sulphur atoms in high vacuum result in an effective dopant for controllable n-type doping. The samples are irradiated using a KrF excimer laser in a N₂ gaseous environment. Secondary ion mass spectrometry (SIMS) measurements show that sulphur is successfully incorporated in the GaAs. The sheet resistance is controlled by adjusting the laser energy fluence and number of laser pulses. Rutherford backscattering spectrometry with channeling (RBS/C) alignment measurement indicates that lattice damage is undetectable for N₂ gas pressures of 760 Torr.     

Optical bistability in fluorescein dyes

Optical bistability has been observed in highly concentrated fluorescein dye solutions and in thin (1 m) doped polymeric films. At concentrations larger than 10^–5 mole/l dye dimers are formed. For fluorescein dye, the dimer-monomer equilibrium constant is 10⁵ l/mole so that most of the dye species are in the dimer form. At 480 nm the dimer absorption cross section is 10^–18 cm²/molecule, while that for the dye monomer molecule is 7.6×10^–17 cm²/molecule. Upon laser excitation dimers dissociate to form monomers thus providing a highly nonlinear laser induced absorption. This high nonlinear absorption coefficient can be utilized for optically bistable response of the dye system.Optical bistability was observed by placing dye solutions or dye thin films inside a Fabry-Perot resonator and exciting it with 480 nm dye laser pulses of 10 ns duration. The effect is more pronounced in 10^–4 mole/l fluorescein than in 10^–6 mole/l fluorescein in which dimer formation is not that efficient.In disodium fluorescein no significant dimer formation is observed even at 10^–3 mole/l dye concentration. The observed bistability both in solution and in thin films can be explained in terms of recent models for optical bistability in nonlinearly absorbing molecular systems.     

Supersaturated Si-As alloy formation by ion implantation and pulsed electron beam annealing

Supersaturated surface alloys produced by very high dose (0.8–2.6×10¹⁷cm^–2) implantation of As-ions into silicon and subsequent pulsed electron-beam annealing have been investigated by means of the channeling technique. The maximum solubility limit of 7×10²¹ As/cm³ has been determined. It exceeds the equilibrium solubility limit by more than a factor of 4. Angular scan measurements indicated that for doses above 1×10¹⁷cm^–2 As atoms are displaced by about 0.12 Å from the regular lattice sites.     

Phosphorus distribution profiles in 100-silicon using a spin-on source at low temperatures

 Incorporation of phosphorus into silicon from a spin-on dopant layer (SOD) at 400 ^°C is described. Annealing experiments were carried out with SOD films deposited on (100) silicon substrates by using the spin-on technique. Conventional heating on a hotplate in normal atmosphere and a temperature range up to 400 ^°C was used to study the dopant incorporation. After removing the SOD-films one part of the silicon substrates was annealed at higher temperatures. Investigations were carried out by SIMS, SAM, XPS, HTEM, stripping Hall and Van der Pauw measurements before and after the high temperature annealing. Chemical phosphorus concentration profiles obtained from low temperature annealed samples showed diffusion depths of 60–80 nm (extrapolated to a substrate doping level of 10¹⁶ cm^-3) and surface concentrations of 10¹⁹–10²⁰ cm^-3. Electron concentration profiles exhibiting maximum values around 2⋅10¹⁹ cm^-3 could be measured on high temperature annealed samples only. Received: 28 March 1996/Accepted: 19 August 1996     

用荧光谱研究GaAs:C的辐射复合过程

本文用荧光时间衰减谱和荧光量子效率测量相结合的方法研究了重掺碳GaAs:C辐射复合特性.GaAs:C是由MOVPE在650℃下生长的,掺杂源采用CBr₄在重掺碳条件下,辐射复合寿命的实验结果比1/BP的预期值大.文章讨论了空穴一空穴、空穴-离化杂质原子相互作用对自发发射速率的影响,并对辐射复合常数B作出了修正.     

Field effect in CdSe single-crystal films

The surface conductivity and effective mobility were studied as functions of the surface potential on CdSe single-crystal films having a conductivity of 1–10^–5 .cm^–1. The surface potential was varied by a constant external field. The formation of a conducting channel at the film surface is governed primarily by the change in the trapping factor as volume traps near the surface are filled. Field-effect data are used to evaluate the parameters of the exponential distribution of volume traps with respect to energy, the effective concentration of small donors, and the absolute values of the surface potential.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp.43–47, March, 1971.     

Optical phonons in nanosize GaAs and AlAs clusters in an InAs matrix

A Raman scattering method is used to investigate structures containing nanosize GaAs and AlAs clusters, which were grown by molecular-beam epitaxy on InAs substrates by the mechanism of self-organized growth under mechanical stress. A large shift of the phonon lines of GaAs and AlAs clusters with respect to the phonon frequencies in the bulk materials (36 and 24 cm⁻¹ for GaAs LO and TO phonons and 55 and 28 cm⁻¹ for AlAs LO and TO phonons, respectively) is observed in the spectra. This fact is explained by the presence of strong mechanical stresses in the GaAs and AlAs clusters. A comparison of the experimental data with the computed strain dependences of the phonon frequencies shows that the GaAs and AlAs clusters are pseudomorphic, i.e., they do not contain dislocations, which lead to relaxation of the mechanical stresses. In the interval between the InAs TO and LO phonon frequencies, the Raman scattering spectra contain features associated with interfacial phonons. The position of these features also attests to the formation of three-dimensional GaAs and AlAs islands and are described well by a continuum dielectric model. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 7, 463–467 (10 October 1999)     

Diffusion of deuterium in GaAs from a molecular gas source

It is shown for the first time that deuterium can diffuse into GaAs from a gaseous source. Experiments performed at 500° C show two-component diffusion profiles with diffusion coefficients in the range 10^–15–4×10^-1cm²s^–1 depending on the conductivity type of the samples. These diffusion coefficients are considerably lower than those determined after RF plasma hydrogenation. Such a slow diffusion process is related to the reaction of molecular deuterium with the sample surface leading to the dissociation of the deuterium molecules.     

Laser-induced free-carrier absorption in Si single crystal

The transmitted energy density in thin single Si crystal, wafers is measured at=1.06 m as a function of the incident energy density for a Nd laser pulse of 30 ns duration. Non-linear effects begin to become important at about 0.3 J/cm². The contribution due to free-carriers is separated from the interband one by using measurements made at low energy density and at different sample temperatures in the 20°–150 °C range. The time dependence of the free-carrier concentration and of the lattice temperature is computed for different values of the Auger constant. The experimental data in the 0.2–2.5 J/cm² energy density range are fitted with an Auger constant of 10^–30 cm⁶s^–1.Work supported in part by M.P.I. and G.N.S.M.-C.N.R.     

Micro-Raman spectroscopy in polycrystalline CuInSe2 formation

The crystalline formation of CuInSe₂ thin films has been investigated using micro-Raman spectroscopy and AES composition analysis. It is confirmed that the Raman peaks are stongly dependent on the surface morphology and the Cu:In:Se ratio. In the films annealed at 315°C, crystalline grains larger than 2 m show Raman peaks at 174 cm^–1 and 258 cm^–1. The In content is very low and the Cu:Se ratio is about 1:1 in these grains. The low In concentration is thought to be due to the formation of In₂O₃ on the surface. On the other hand, random structures of 1–2 m grains found in films annealed at temperatures below 305°C show peaks at 174 cm^–1 and 186 cm^–1 instead of 258 cm^–1 and have a Cu:In:Se ratio of 1:1:3–4. Thus the 186 cm^–1 peak is thought to be related to a Cu, In-deficient phase when compared to stoichiometric CuInSe₂. The optimum annealing condition was found by analyzing the Raman spectra and composition of different crystalline CuInSe₂ grains. Films annealed under this condition exhibited a clear Raman peak at 174 cm^–1 and consisted of clusters of crystals less than 1 m in size.