Quenching of EL2 defect-induced luminescence in gallium arsenide by copper atoms

It is shown that the introduction of copper atoms into gallium arsenide crystals containing EL2 antisite defects results in virtually complete vanishing of the EL2-induced luminescence bands with radiation maxima at hv _m =0.63 and 0.68 eV. This occurs as a result of the deactivation of the EL2 defects as a result of their interaction with copper atoms, which account for the formation of electrically inactive EL2-Cu complexes. Fiz. Tekh. Poluprovodn. 31, 1045–1048 (September 1997)     

Effect of electron and neutron bombardment on the orange luminescence spectra of not specially doped and copper-doped cadmium sulfide single crystals

CdS single crystals which were not specially doped and which were doped with copper (N _Cu=10¹⁸ cm⁻³) have been investigated. It is concluded on the basis of an analysis of the dose dependences of the orange luminescence intensity (λ _M=605 nm) of “pure” and doped samples upon bombardment by electrons with E=1.2 MeV and by fast reactor neutrons that the centers responsible for this luminescence are complex in nature. They consist of interstitial cadmium atoms and oxygen atoms. Electron bombardment of CdS:Cu single crystals results in the formation of new centers which are responsible for luminescence with λ _M=570 and 545 nm. Fiz. Tekh. Poluprovodn. 31, 390–392 (April 1997)     

Influence of fast-neutron irradiation on the intensity of the copper-related luminescence band at hν m =1.01 eV in n-type GaAs

The influence of neutron irradiation (the energy E=2 MeV and the dose Φ=10¹³–10¹⁵cm⁻²) and subsequent anneals (the annealing temperature T _a =400–700 °C and the annealing time is 30 min) of n-type GaAs(Te,Cu) crystals with an initial carrier concentration n ₀=2×10¹⁸ cm⁻³ on the intensity of the copper-related luminescence band with an emission maximum at hν _m =1.01 eV is studied. A significant irradiation-induced increase in the intensity of the band is observed. It is attributed to a radiation-stimulated increase in the concentration of emitting centers (Cu_Ga V _As pairs) as a result of the effective interaction of interstitial copper atoms with irradiation-induced gallium (V _Ga) and arsenic (V _As) vacancies, as well as V _Ga V _As divacancies. Fiz. Tekh. Poluprovodn. 31, 1171–1173 (October 1997)     

Defect-formation processes in silicon doped with manganese and germanium

Deep-level transient spectroscopy has been used to study the effect of Ge atoms on the behavior of Mn in Si. It is shown that Ge atoms introduced into Si during growth manifest no electrical activity, even though their concentration is rather high: 10¹⁶–10¹⁹ cm⁻³. It is established that the presence of Ge atoms in the Si lattice enhances the efficiency of the formation of the deep levels E _c -0.42 eV and E _c -0.54 eV, which are associated with Mn in the Si lattice: the concentration of these deep levels in Si〈Ge, Mn〉 samples is a factor of 3–4 greater than in Si〈Mn〉. It is found that the presence of Ge atoms stabilizes the properties of the Mn levels in Si: They anneal more slowly than in Si〈Mn〉 by a factor of 5–6. It is assumed that the detected effects are associated with the features of the defect structure of Si doped with Ge and Mn. Fiz. Tekh. Poluprovodn. 32, 676–678 (June 1998)     

Structural and Passivative Behaviors of Cu(In) Thin Film

This investigation prepares a low-resistivity and self-passivated Cu(In) thin film. The dissociation behaviors of dilute Cu-alloy thin films, containing 1.5–5at.%In, were prepared on glass substrates by a cosputter deposition, and were subsequently annealed in the temperature range of 200–600 °C for 10–30 min. Thus, self-passivated Cu thin films in the form In₂O₃/Cu/SiO₂ were obtained by annealing Cu(In) alloy films at an elevated temperature. Structural analysis indicated that only strong copper diffraction peaks were detected from the as-deposited film, and an In₂O₃ phase was formed on the surface of the film by annealing the film at an elevated temperature under oxygen ambient. The formation of In₂O₃/Cu/SiO₂ improved the resistivity, adhesion to SiO₂, and passivative capability of the studied film. A dramatic reduction in the resistivity of the film occurred at 500 °C, and was considered to be associated with preferential indium segregation during annealing, yielding a low resistivity below 2.92 μΩcm. The results of this study can be potentially exploited in the application of thin-film transistor–liquid crystal display gate electrodes and copper metallization in integrated circuits.     

The structure of high-temperature blue luminescence centers in zinc selenide and mechanisms of this luminescence

The characteristic features of temperature quenching of the intensity of the edge luminescence bands of n-ZnSe crystals annealed in different media (vacuum, Zn, Se) are investigated a wide temperature range. A change in the mechanisms of high-temperature exciton luminescence in the short-wavelength region of the spectrum (443 nm) with increase in temperature of the crystal is observed. It is shown that the nature of temperature quenching of the long-wavelength edge luminescence band (458 nm) is evidence of dissociation of associative luminescence centers with increase in the sample temperature. Fiz. Tekh. Poluprovodn. 32, 178–181 (February 1998)     

Conductivity relaxation in coated porous silicon after annealing

A study has been carried out of the effect of a brief anneal at 450–550 °C on the conductivity of porous silicon coated with a metallic film. Porous silicon, formed on p-and n-type substrates, had porosities of 16–40% and 5–10%, respectively. It has been shown that for anneals at 500 and 550 °C porous silicon on p-type Si is converted to the highly conducting state. The conductivity relaxation in coated porous silicon layers on p-Si after annealing is described. The results are analyzed from the point of view of a model of passivation of the impurity atoms by hydrogen. It is shown that after annealing an aluminum-〈porous silicon〉 junction possesses a rectifying property. The potential barrier parameters for Al-〈porous silicon〉 junctions on p-and n-type substrates are determined. Fiz. Tekh. Poluprovodn. 33, 476–480 (April 1999)     

Effect of superstoichiometric components on the spectral and kinetic characteristics of the luminescence of ZnSe crystals with isovalent impurities

The spectral and kinetic parameters of the X-ray luminescence of ZnSe crystals doped with Zn, Se, and Te were investigated during the growth process at temperatures in the range 80–500 K, and also after annealing in Zn vapor. ZnSe crystals grown from a stoichiometric mixture, or mixture containing chalcogenide impurities, typically produce the minimum level of afterglow and a rapid rise of X-ray luminescence, as well as a shift of its peak from the infrared region toward shorter wavelengths after annealing in zinc. ZnSe crystals grown from material with excess of Zn have a relatively low X-ray luminescence yield and a substantial level of afterglow. It is assumed that the growth of Te-activated crystals is accompanied by the development of thermally stable complexes of the form V _ZnTe_Se that act as radiative recombination centers. The introduction of excess Zn into the initial mixture produces a reduction in the concentration of V _Zn and, hence, in the concentration of radiative recombination centers. It is shown that, for free-electron concentrations n<10¹⁸ cm⁻³, the afterglow time constant τ can be described as a function of n by a model of radiative recombination that involves a single impurity level, whereas for n>10¹⁸ cm⁻³, the time constant decreases with increasing n, which cannot be explained in terms of the simple model. It is suggested that radiative recombination centers of a new type are produced as a result of prolonged annealing in Zn vapor. Fiz. Tekh. Poluprovodn. 31, 1211–1215 (October 1997)     

Analysis of changes in the intensity of intrinsic luminescence after diffusion of copper into semi-insulating undoped gallium arsenide crystals

The effect of copper diffusion into semi-insulating undoped GaAs crystals on the intensity of intrinsic luminescence is analyzed. It is shown that diffusion of copper into semi-insulating undoped GaAs crystals can lead either to an increase or a decrease in the intensity of intrinsic luminescence. Analytic relations, which connect the magnitude and sign of the effect with recombination parameters in these crystals, and also with the intensity of the excitation luminescence, are obtained. Fiz. Tekh. Poluprovodn. 32, 570–573 (May 1998)     

Stabilization of the physical properties of CdxHg1−x Se solid solutions doped with iron

The electrical and galvanomagnetic properties of Cd_xHg_1−x Se crystals (x=0.23) doped with iron in various concentrations are investigated in the temperature range 77–400 K and in magnetic fields up to 1.6 T. It is established that iron introduced into the crystal host stabilizes its physical properties. It is shown that annealing the samples in selenium vapor has only a small effect on their physical characteristics. Fiz. Tekh. Poluprovodn. 32, 782–785 (July 1998)     

Modification of the electron spectrum and vibrational properties of amorphous carbon by copper doping

The near-gap electron spectrum and the effective charge distribution in graphite-like carbon nanoclusters of simple geometry in a-C: H containing a single Cu atom are calculated in the tight-binding approximation. Only the coupling between π electrons of the constituent C atoms and one valence s electron of the Cu atom is taken into account. The binding energy of the Cu atom in the clusters and the static dipole moment of the clusters are calculated. The results are invoked to interpret the experimentally observed activation of the Raman G band in the IR spectrum of a-C: H: Cu as a consequence of a lowering of the symmetry of the graphite-like clusters due to copper intercalation. Experimental data on the time dependence of the G band intensity during isothermal annealing of a-C: H: Cu are presented. The data suggest the possibility of reversible transfer of Cu atoms between the impurity states in the copper-carbon clusters and the impurity states in the purely copper clusters. The average activation energies of direct and reverse transfer are estimated from the experiment. Fiz. Tekh. Poluprovodn. 32, 931–938 (August 1998)     

Nitrogen divacancies — The possible cause of the “yellow band” in the luminescence spectra of GaN

A strong analogy is demonstrated between the well-known impurity complex NN₁ in GaP consisting of a pair of nearest-neighbor isovalent nitrogen impurity atoms in the nitrogen-doped gallium phosphide lattice (GaP: N), and the divacancy complex of nearest-neighbor vacancies in the nitrogen sublattice of gallium nitride. This divacancy or complexes of this divacancy with impurities may be the cause of the “yellow band” in the luminescence spectra of GaN. This work was presented at a session of the Electrochemical Society (Paris, September 1997 by A. E. Yunovich, in Proceedings of the Second Symposium on III–V Nitride Materials and Processes, Electrochemical Society (Pennington, New Jersey, 1998), Vol. 98-02, p. 258. Fiz. Tekh. Poluprovodn. 32, 1181–1183 (October 1998)     

The nature of manganese luminescence centers in zinc sulfide single crystals

This paper discusses how the luminescence-excitation method affects the spectral content of the emission in ZnS: Mn single crystals. It shows that the nearest neighborhood of the Mn²⁺ ions is associated with the elementary emission bands having maxima at the wavelengths λ_m=557, 578, 600, 616, and 638±2 nm in zinc sulfide crystals with different manganese concentrations. Fiz. Tekh. Poluprovodn. 32, 673–675 (June 1998)     

Calculation of the Schottky barrier height at the early stage of formation of the (silicon carbide)-(metallic submonolayer) contact

The position of the local and quasi-local states of metal atoms (alkali metals, group-III metals, the copper group) adsorbed on the surface of 6H-SiC are calculated within the framework of the extended Anderson-Halstane model of the semiconductor density of states. The results of these calculations are compared with the experimental data on Schottky barriers. Fiz. Tekh. Poluprovodn. 32, 68–71 (January 1998)     

Molecular-beam epitaxy of a strongly lattice-mismatched heterosystem AlN/Si(111) for application in SAW devices

The results of using molecular-beam epitaxy for growing piezoelectric AlN films on Si (111) substrates suitable for device applications are reported. The technological conditions for growth of stoichiometric AlN by controlling the surface reconstruction occurring under various thermodynamic conditions on the growth surface are determined. The films of the hexagonal polytype of AlN possess high crystalline perfection and an atomically smooth epitaxial surface. The mechanism for relaxation of the AlN crystal lattice over a distance of one monolayer from the heterojunction is found. It is demonstrated that the AlN film is piezoelectric. Investigations of the temporal characteristics of a SAW attest to a low level of scattering of the wave during propagation. The electromechanical coupling constant is measured in interdigital transducer geometry (λ=16 mm) and is found to be 0.07 % at a frequency f=286 MHz, in good agreement with the theoretical value for a 1.04-μm-thick AlN film. Fiz. Tekh. Poluprovodn. 33, 1372–1378 (November 1999)     

Impact ionization luminescence of InGaN/AlGaN/GaN p-n-heterostructures

The luminescence spectra of InGaN/AlGaN/GaN p-n heterostructures with reverse bias sufficient for impact ionization are investigated. The injection luminescence of light-emitting diodes with such structures was examined earlier. A strong electric field is present in the InGaN active layer of the heterostructures, and for small reverse bias the tunneling component of the current predominates. Avalanche breakdown commences at voltages V _th>8–10 V, i.e., ∼3E _g , (E _g is the width of the band gap) in the absence of lightly doped structures. The luminescence spectra have a short-wavelength edge corresponding to the width of the GaN band gap (3.40 eV) and maxima in the region 2.60–2.80 eV corresponding to the maxima of the injection luminescence spectra in the active layer. The long-wavelength edge of the spectra in the region 1.7–1.8 eV may be associated with deep recombination levels. Mechanisms of recombination of the hot electron-hole plasma in the strong electric fields of the p-n heterostructures are discussed. Fiz. Tekh. Poluprovodn. 32, 63–67 (January 1998)     

The structure and optical properties of nanocrytalline lead sulfide films

The crystal structure of lead sulfide (PbS) films produced by chemical deposition onto a glass substrate is studied by X-ray diffraction analysis. The thickness of the synthesized films is ∼120 nm, the dimensions of the regions of coherent scattering are 70–80 nm, and the magnitude of microstrains is ∼0.20%. It is established that the crystal structure of the synthesized PbS films and of the same films annealed at the temperature 293–423 K is cubic (space group Fm 3m) and corresponds to the D0₃ type that differs from the B1 type typical of coarse-grained PbS. In the cubic structure of the PbS nanofilms, there is a latent nonstoichiometric distribution of S atoms and vacancies among octahedral sites 4(b) and tetrahedral positions 8(c). The optical transmittance of the nanocrystalline PbS films is measured in the wavelength range from 200 to 3270 nm. The most pronounced variations in the transmittance is observed in the wavelength range from 700–800 to 1600–2000 nm (corresponding to the photon energy range from ∼1.8 to ∼0.7 eV). It is established that the band gap E _g is 0.83–0.85 eV, i.e., it is larger than the band gap of single-crystal PbS, 0.41 eV.     

Calculation of 2p levels for thermal double donors in silicon

A two-center model is developed to explain the electronic structure of thermal double donors (TDD) in silicon. Calculations of 2p levels of singly ionized TDD’s are performed in the effective mass approximation. From a comparison of the calculated results with the experimental data, the internuclear distance between the two electrically active atoms is evaluated as 0.75–0.95 nm for the TDD1–TDD3 and 1.35–1.75 nm for the next four species: TDD4–TDD7. Fiz. Tekh. Poluprovodn. 31, 961–965 (August 1997)     

Influence of the initial boron doping level on the boron atom distribution arising as a result of heat treatment in silicon implanted with boron ions

The dependence of the boron distribution on the initial boron concentration in the range (1–9)×10¹⁹ cm⁻³ was investigated by secondary-ion mass-spectrometry (SIMS) after heat treatment of boron-ion implanted silicon at 900 °C. It was found that when the initial boron concentration exceeds the solubility limit at the annealing temperature used, two additional peaks arise in the boron concentration profiles at the boundaries of the ion-implantation disordered region. It is suggested that their appearance in these regions at high doping levels is due to clustering of excess interstitial impurity atoms not built into the lattice sites following displacement of boron atoms from the lattice sites by intrinsic interstitials that leave the disordered region. Fiz. Tekh. Poluprovodn. 32, 417–420 (April 1998)     

Optical properties of silicon-doped (100) GaAs layers grown by molecular-beam epitaxy

The photoluminescence spectra of (100) GaAs layers, both undoped and doped with silicon, is investigated at T=77 K. It is found that along with the B-band, which corresponds to interband radiative recombination, the spectra of doped layers also exhibit a so-called Si-band located near hν⋍1.4 eV. In multilayer δ-doped structures, an additional band appears in the region hν⋍1.47–1.48 eV, which is called here the δ-band. The dependence of the energy positions, intensities, and shapes of these photoluminescence bands on the doping dose N _Si, laser excitation power, and temperature are investigated. It is shown that the Si-band is caused by optical transitions between the conduction band and a deep acceptor level (∼100 meV) connected with Si atoms on As sites. It is also established that the dependences of the shape and intensity of the δ-band on temperature and photoluminescence excitation power are identical to the corresponding dependences for the B-band. The behavior of the δ-band in the photoluminescence spectra is viewed as evidence of quantum-well effects in the δ-doped structures. Fiz. Tekh. Poluprovodn. 32, 1060–1063 (September 1998)