Beryllium-hydrogen and zinc-hydrogen shallow acceptor complexes in germanium

New shallow acceptor complexes with hydrogenically-spaced excited states have been discovered in intentionally-doped crystals of otherwise ultra-pure germanium. The doping consists of >10¹⁴ cm⁻³ of group II impurities, and the crystals were grown under hydrogen atmosphere. The identification proposed in this paper is that of a hydrogen-group II impurity complex, with piezospectroscopic behavior of a 〈111〉-oriented defect.     

Terahertz electroluminescence under conditions of shallow acceptor breakdown in germanium

The spectrum of spontaneous terahertz electroluminescence was obtained near the breakdown threshold of a shallow acceptor (Ga) in germanium. The emission spectra were recorded by the Fourier spectroscopy method at a temperature of ～5.5–5.6 K. The emission spectrum exhibits narrow lines with maxima at ～1.99 THz (8.2 meV) and ～2.36 THz (9.7 meV), corresponding to the optical transitions of nonequilibrium holes from the excited impurity states to the ground state of impurity center. A broad line with a maximum at ～3.15 THz (13 meV) corresponding to the hole transitions from the valence band to the impurity ground state is also seen in the spectrum. The contribution of the hole transitions from the states of the valence band increases upon an increase in the electric-field strength. Simultaneously, the optical transitions of nonequilibrium holes between the subbands of the valence band appear in the emission spectrum. The integral terahertz-emission power is ～17 nW per 1 W of the input power.     

Effect of uniaxial stress on shallow acceptor states in silicon and germanium

Summary Energies and wave functions of shallow acceptor states under uniaxial stress have been computed in silicon and germanium. Calculations have been carried out up to high stress values within the effective-mass approximation. The full cubic crystal symmetry has been taken into account. The splittings of the ground state and of the odd-parity excited states, the relative intensities of optical transitions, as well as the energies of odd states for high stress values have been found to be in agreement with the results of optical measurements. However, results for even-parity excited states cannot as yet be compared with present experiments.

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Riassunto Le energie e le funzioni d'onda degli stati accettori poco prodondi sotto tensione uniassiale sono state calcolate per silicio e germanio. I calcoli sono stati fatti fino ad alti valori di tensione nell'approssimazione della massa efficace. è stata presa in considerazione la simmetria cubica completa del cristallo. Gli sdoppiamenti dello stato fondamentale, degli stati eccitati a parità dispari, le intensità relative delle transizioni ottiche, cosí come le energie degli stati dispari per alti valori di tensione sono in accordo con i risultati delle misurazioni ottiche. Tuttavia, i risultati per gli stati eccitati a parità pari non possono ancora essere confrontati con gli esperimenti attuali.

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Реэюме Вычисляются энергии и волновые функции мелких акцепторных состояний при одноосном напряжении в кремнии и германии. Вычисления проводятся в рамках приближения эффективной массы вплоть до больших значений напряжений. Учитывается полная кубическая симметрия кристалла. Получается, что расщепления основного состояния и нечетных возбужденных состояний, относительные интенсивности оптических переходов, а также энергии нечетных состояний при больших значениях напряжений согласуются с результатами оптических измерений. Однако, результаты для четных возбужденных состояний не могут быть еще сравнены с имеющимися экспериметами.

     

Magnetic moment relaxation of a shallow acceptor center in heavily doped silicon

Results of studying the temperature dependence of the residual polarization of negative muons in crystalline silicon with germanium (9×10 ¹⁹ cm ^?3 ) and boron (4.1×10 ¹⁸ , 1.34×10 ¹⁹ , and 4.9×10 ¹⁹ cm ^?3 ) impurities are presented. It is found that, similarly to n-and p-type silicon samples with impurity concentrations up to ～10 ¹⁷ cm ^?3 , the relaxation rate ν of the magnetic moment of a _μ Al acceptor in silicon with a high impurity concentration of germanium (9×10 ¹⁹ cm ^?3 ) depends on temperature as ν～T ^q , q≈3 at T=(5–30) K. An increase in the absolute value of the relaxation rate and a weakening of its temperature dependence are observed in samples of degenerate silicon in the given temperature range. Based on the experimental data obtained, the conclusion is made that the spin-exchange scattering of free charge carriers makes a significant contribution to the magnetic moment relaxation of a shallow acceptor center in degenerate silicon at T?30 K. Estimates are obtained for the effective cross section of the spin-exchange scattering of holes (σ _h ) and electrons (σ _e ) from an Al acceptor center in Si: σ _h ～10^?13 cm² and σ _e ～8×10^?15 cm² at the acceptor (donor) impurity concentration n _a (n _d )～4×10¹⁸ cm^?3.     

Piezospectroscopy of the triple acceptor neutral copper in germanium

Experimental and theoretical results are presented for the behaviour of the optical absorption lines of neutral copper, a triple acceptor, in germanium under applied uniaxial compression. The ground state for the three equivalent holes is found to be the four-fold degenerate Λ₈ state of $\text{T}{}_{\mathrm{d}}$. The interpretation of the results requires that, for F6〈111〉, there be no splitting of either the ground state or the excited state of the D-line. However, this interpretation produces a violation of the predicted selection rules for the G components with F6〈100〉.     

Sum rule for the intraband absorption and the oscillator strengths of the optical transitions in the shallow acceptor impurities in germanium

The sum rule for the cross-section of intraband optical absorption is derived in the effective-mass approximation. A numerical method of calculation of the wave functions of the shallow acceptors in the spherical approximation is developed. The oscillator strengths of several lines in the spectra of the group III impurities in germanium are determined.     

Polarization of the terahertz radiation of uniaxially compressed p germanium at the electrical breakdown of a shallow acceptor impurity

The spectral and polarization investigations of spontaneous terahertz radiation under the conditions of the electrical breakdown of shallow acceptors (gallium) in germanium crystals have been reported. The radiation spectra of crystals uniaxially compressed in the [111] direction at a pressure of about 3 kbar, as well as undeformed crystals, have been measured at T = 5 K using a Fourier spectrometer with step scanning. The polarization of radiation has been estimated for transitions of holes between various states of a shallow acceptor in uniaxially compressed germanium. To identify the observed radiation lines, their experimental energies and polarizations have been compared to the respective calculated values. The spectral lines corresponding to the transitions of holes from the resonance state to the excited states of acceptors have been identified.     

Impact ionization of deep acceptor gold in germanium

We observed the dependence of conductivity on an applied high electric field in compensated gold-doped germanium between 77 and 300K. A slight decrease in conductivity, mainly due to the field-dependent carrier mobility, is followed by a relatively large increase in conductivity. The magnitude of this increase depends on the lattice temperature, being larger at low temperatures, and on the compensation ratio. The increase in conductivity is supposed to be due to impact ionization of the frozen-out neutral acceptor gold in the strong electric field. This interpretation is supported by the temperature dependence of the hole concentration in the gold-doped germanium.     

Relaxation dynamics and photoconductivity inp-type germanium

The relaxation of holes inp-Ge excited by CO₂ laser radiation is analyzed in a detailed cascade model. The scattering times are taken in part from theory and from recent saturation-spectroscopic measurements. From this model we calculate the photoconductive response quantitatively. Experimentally we observe the conductivity change induced by single ns CO₂ laser pulses and find good agreement with the predictions.     

The relaxation rate of the magnetic moment of a shallow acceptor center as a function of impurity concentration in silicon

A study is made into the temperature dependence of residual polarization of negative muons in crystalline silicon with the concentration of impurity of the n-and p-types ranging from 8.7×10¹³ to 4.1× 10¹⁸ cm^?3. The measurements are performed in a magnetic field of 1000 G transverse to the muon spin, in the temperature range from 4.2 to 300 K. The form of the temperature dependence of the relaxation rate v of the magnetic moment of the μAl⁰ acceptor in silicon is determined. For a nondegenerate semiconductor, the relaxation rate depends on temperature as v ∝ T ^q (q ≈ 3). A variation in the behavior of the temperature dependence and a multiple increase in the relaxation rate are observed in the range of impurity concentration in excess of 10¹⁸ cm^?3. The importance of phonon scattering and spin-exchange scattering of free charge carriers by an acceptor from the standpoint of relaxation of the acceptor magnetic moment is discussed. The constant of hyperfine interaction in an acceptor center formed by an atom of aluminum in silicon is estimated for the first time: |A _hf (Al)/2π| ～ 2.5×10⁶s^?1.     

Low-temperature intracenter relaxation times of shallow donors in germanium

The relaxation times of localized states of antimony donors in unstrained and strained germanium uniaxially compressed along the [111] crystallographic direction are measured at cryogenic temperatures. The measurements are carried out in a single-wavelength pump–probe setup using radiation from the Novosibirsk free electron laser (NovoFEL). The relaxation times in unstrained crystals depend on the temperature and excitation photon energy. Measurements in strained crystals are carried out under stress bar S > 300, in which case the ground-state wavefunction is formed by states belonging to a single valley in the germanium conduction band. It is shown that the application of uniaxial strain leads to an increase in the relaxation time, which is explained by a decrease in the number of relaxation channels.     

Resonant states of shallow acceptors in uniaxially deformed germanium

The states of shallow acceptors in uniaxially deformed germanium are studied theoretically. A non-variational numerical computational method is developed for determining the energy and wave functions of localized states of holes in the acceptor field as well as the states of the continuous spectrum (including resonant impurity states). The dependence of the energy of the lower resonant state on strain is studied. It is found that this state is formed from the excited 4Γ ₈ ⁺ state with a binding energy of 1.3 meV (in the absence of deformation) and not from the ground state. The results presented in this work may be useful in the study of the conditions for the generation of far IR radiation in deformed p-Ge, which involves optical transitions between resonant and localized acceptor states.     

硅中浅杂质的激光感应光电导谱

首次采用光子能量小于硅中浅受主杂质电离能的可调谐远红外激光器作为激发源,获得了硅中浅受主杂质的光电导谱.可调谐半导体远红外激光器的调谐范围为380～500cm~(-1),光子流密度约10~(18)/cm~2·sec,用双光子跃迁对光电导谱进行了解释.对于Si:Al样品,光电导谱中的双峰分别相应于2P~1和2P~2中间态的双光子共振跃迁.也观察到了双光子透明的反共振现象.     

高纯锗中浅受主的光热电离光谱

在液氦温度附近, 运用傅里叶变换光谱以及与之相连的磁光光谱系统, 对室温电阻率约为50Ω·cm的p型高纯锗样品进行了高灵敏度的光热电离光谱的研究.从实验上确定了高纯锗样品中浅杂质光热电离的最佳温度范围, 在该温度范围内测量了样品的光热电离光谱, 指出该样品中主要杂质为浅受主硼与铝. 对杂质谱线发生分裂的两种原因, 补偿性杂质导致的快速复合以及随机应力等, 进行了分析讨论. 关键词： 高纯锗 光热电离光谱 元素半导体中的杂质和缺陷能级     

高纯锗中浅受主的光热电离光谱

在液氦温度附近, 运用傅里叶变换光谱以及与之相连的磁光光谱系统, 对室温电阻率约为50Ω·cm的p型高纯锗样品进行了高灵敏度的光热电离光谱的研究.从实验上确定了高纯锗样品中浅杂质光热电离的最佳温度范围, 在该温度范围内测量了样品的光热电离光谱, 指出该样品中主要杂质为浅受主硼与铝. 对杂质谱线发生分裂的两种原因, 补偿性杂质导致的快速复合以及随机应力等, 进行了分析讨论.     

Magnetic moment of an acceptor center in cubic semiconductors

The magnetic field-induced splitting of the ground-state spin levels of an acceptor center, described by superposition of the Coulomb and the central-cell potentials, has been calculated for diamond-type. An analytic expression for the g factor obtained in the zero-radius potential approximation depends only on the light to heavy hole mass ratio. It is shown that the differences between the values of the g factor for the limiting cases of purely Coulomb and zero-radius potentials do not exceed 5%, thus permitting one to use this analytic expression for estimates. Fiz. Tverd. Tela (St. Petersburg) 39, 58–60 (January 1997)