Temperature dependence of the tunable luminescence of GaAs doping superlattices

Doping superlattices show tunable optical and electrical properties due to the space charge induced separation of photoexcited or electrically injected carriers. We have investigated the tunable luminescence in GaAs doping superlattices of doping levels n=1×10¹⁸cm⁻³ and n=4×10 ¹⁸cm⁻³ as function of excitation density and sample temperature. The temperature dependence of the tunability was investigated in the range between 4 and 700K, and we found the critical transition temperatures T₀ at 90 and 460K for the low and high doped samples, respectively. The results verify the theoretical prediction concerning the transition temperature at which the luminescence changes from full to zero tunability.     

Temperature,injection level,and frequency dependences of the luminescence in lightly - and heavily-doped CdTe:In

The temperature dependence, injection level dependence, and modulation frequency response of cathodoluminescence have been measured in Te-rich CdTe:In for materials with In concentrations ranging from 3 × 10¹⁵cm^?3 to 1 × 10¹⁸cm^?3. In lightly-doped material, the 80 K luminescence shows sharp band-edge emission near 1.57 eV and a broad impurity-defect band near 1.4 eV. As temperature increases, the 1.4 eV band quenches out, leaving only the band-edge emission. In heavily-doped material, the band- edge emission is absent and the 80 K luminescence shows only the 1.4 eV band. As the temperature increases from 80 K to 300 K, the 1.4 eV band does not quench out but rather undergoes a complex evolution into a long tail on the band-edge emission which begins to appear at approximately 140 K. At a temperature of 200 K, where the luminescence of the heavily-doped material consists of a broad but structured band approximately 0.2 eV in width, frequency response measurements indicate that band-to-band transitions contribute to the high-energy part of the broad luminescence while the remainder of the band results from slower transitions. The frequency and temperature dependences suggest that the luminescence involves an impurity level that has merged with a band edge at an In concentration of $\text{1 × 10}{}^{18}\text{cm}{}^3$. We interpret this behavior as suggesting that the 1.4 eV luminescence in Te-rich CdTe:In results from a partially-forbidden transition between conduction band and a deep acceptor level rather than from an intracenter type of transition.     

Hysteresis effect and surface energy of drops in silicon

We report here the observation of the hysteresis effect of the drop luminescence in silicon at the temperature of 6.6 K. Hysteresis ratios up to 2.1 have been registered. The surface energy σ of drops is deduced from the measurement of the energy shift of the drops luminescence at low pumping level. The results yield: σ = (125±60) × 10^?4ergcm^?2.     

Dependence of lifetime on design parameters of an nipi doping superlattice: Results of self-consistent calculations

This paper presents a scheme for calculating recombination lifetimes in a doping superlattice at arbitrary temperatures and forward biases. The scheme involves the self-consistent calculation of sub-band energies, populations and envelope functions, followed by the calculation of lifetime using overlap integrals. Results of these calculations are then presented for a variety of combinations of layer thicknesses and dopings, all at a temperature of 300 K and a forward bias of 1 V. Our results give room temperature lifetimes as high as ∼30 ms for n and p layer thicknesses of 750 Å each, i-layer thickness of 50 Å, and dopings in the n and p layers of 2×10¹⁸ cm⁻³.     

Ground-state depleted solid-state lasers: principles,characteristics and scaling

A novel class of rare-earth-doped solid-state lasers is described. The ground-state depleted laser is pumped by an intense (more than tens of kW cm⁻²) narrow-band (less than a few nm) laser source and is characterized by: (1) an unusually low laser ion doping density (5 to 10×10¹⁸ion cm⁻³), (2) an unusually large fractional excited population inversion density (4 to 8×10¹⁸ ion cm⁻³, or >75%), (3) a gain element that is optically thick at the pump wavelength and (4) a gain element that has a substantially uniform gain distribution due to a bleaching of the pump transition at the pump intensity utilized. These features enable efficient room-temperature operation of rare-earth-ion laser transitions terminating on the ground manifold. The relationships between laser parameters (cross-sections, saturation fluences and fluxes, bleaching wave velocities, etc.) are given and laser performance scaling relationships are presented and discussed.

     

掺铍GaAs量子阱的光致荧光

测量了掺铍的,阱宽约为10nm的GaAs量子阱在4.2K的光致荧光。掺杂浓度分别为1×10¹⁷和5×10¹⁸cm^-3。测量结果表明:对于无规掺杂,局域在阱中心的铍的状态密度与导带电子从n=1量子能级到阱中心中性铍的跃迁概率的乘积大于对应于介面铍的乘积。另外,实验结果也表明:当掺杂浓度升高时,由于带隙收缩的影响,阱中心铍的电离能减小。     

Crystallinity and interdiffusion in InP/InGaAs quantum wells grown by Hydride VPE

This paper reports the results of a study on interfacial quality and thermal interdiffusion for InP/InGaAs Quantum Wells (QW) grown by hydride VPE. By controlling well layer as thin as 25 Å, it was estimated that island and valley, whose height was one monolayer and whose lateral size was one third of exciton radius, existed at the interface. For the first time, interdiffusion coefficients for InP/InGaAs QW were obtained from 77K PL peak energy shift. Typical values were 2.5×10⁻¹⁹ cm²/sec and 1.5×10⁻¹⁸ cm²/sec for the annealing temperature of 700°C and 750°C, respectively. These values are over 10² times larger than that in AlGaAs/GaAs QW, and less 10⁻² times smaller than that in InAlAs/InGaAs QW.     

Complex impedance study of annealing effects on polycrystalline KDP conductivity

Annealing effects on the conductivity of KDP (KH₂PO₄) samples prepared either by melting under slight pressure (5.7 kgf/cm²) or by powder compression (1.3 × 10³kgf/cm²) were studied in air by complex impedance spectroscopy. In both cases, annealing at 423 K reduces the conductivities to constant values: from 6.2 × 10 ⁻⁶ to 1.6 × 10⁻⁷ Ω⁻¹ cm⁻¹ for samples prepared by melting and from 1.9 × 10^∼7 to 6.1 × 10^∼8 Ω⁻¹ cm⁻¹ for samples prepared by compression. Heating KDP at about 500 K significantly modifies its electric properties. Two relaxation processes are observed after this treatment. One of them is associated with a fairly strong dielectric polarizability. A small conductivity jump is observed close to 440 K.     

Type III - Type I transition and strain-effect in Hg1−xCdxTeCdTe and Hg1−xZnxTeCdTe superlattices

In this paper, the results of Hg_1−xZn_xTeCdTe strained layer superlattices grown by MBE are reported, and compared to Hg_1−xCd_xTeCdTe superlattices. Both Type III and Type I Hg_1−xZn_xTeCdTe superlattices with different strain have been grown on CdTe(111)B/GaAs(100) and CdTe(100)/GaAs(100) substrates and characterized by electron, X-ray diffraction, infrared transmission and Hall measurements. The values of hole mobility between 5×10³ up to 2×10⁴cm²v⁻¹s⁻¹ at T = 23K along (111)B growth orientation and up to 4.9×10⁴cm²v⁻¹s⁻¹ at T = 5K along (100) growth orientation are obtained for Type III superlattices whereas in Type I superlattices, the hole mobility is between 200–300cm²v⁻¹s⁻¹. This drastic change in the hole mobility between Type III and Type I superlattices along with the role of the strain are discussed in this paper.     

Exciton spectra and electrical conductivity of epitaxial silicon-doped GaN layers

Optical spectra and electrical conductivity of silicon-doped epitaxial gallium nitride layers with uncompensated donor concentrations N _D — N _A up to 4.8 × 10¹⁹ cm^?3 at T ≈ 5 K have been studied. As follows from the current-voltage characteristics, at a doping level of ～3 × 10¹⁸ cm^?3 an impurity band is formed and an increase of donor concentration by one more order of magnitude leads to the merging of the impurity band with the conduction band. The transformation of exciton reflection spectra suggests that the formation of the impurity band triggers effective exciton screening at low temperatures. In a sample with N _D — N _A = 3.4 × 10¹⁸ cm^?3, luminescence spectra are still produced by radiation of free and bound excitons. In a sample with N _D — N _A = 4.8 × 10¹⁹ cm^?3, Coulomb interaction is already completely suppressed, with the luminescence spectrum consisting of bands deriving from impurity-band-valence band and conduction-band-valence band radiative transitions.     

Optical and electrical properties of GaN: Si-based microstructures with a wide range of doping levels

The optical and electrical properties of silicon-doped epitaxial gallium nitride layers grown on sapphire have been studied. The studies have been performed over a wide range of silicon concentrations on each side of the Mott transition. The critical concentrations of Si atoms corresponding to the formation of an impurity band in gallium nitride (～2.5 × 10¹⁸ cm^?3) and to the overlap of the impurity band with the conduction band (～2 × 10¹⁹ cm^?3) have been refined. The maximum of the photoluminescence spectrum shifts nonmonotonically with increasing doping level. This shift is determined by two factors: (1) an increase in the exchange interaction leading to a decrease in the energy gap width and (2) a change in the radiation mechanism as the donor concentration increases. The temperature dependence of the exciton luminescence with participating optical phonons has been studied. The energies of phonon-plasmon modes in GaN: Si layers with different silicon concentrations have been measured using Raman spectroscopy.     

Temperature-dependent 29Si NMR resonance shifts in lightly- and heavily-doped Si:P

Careful NMR measurements on a very lightly-doped reference silicon sample provide a convenient highly precise and accurate secondary chemical shift reference standard for ²⁹Si MAS-NMR applicable over a wide temperature range. The linear temperature-dependence of the ²⁹Si chemical shift measured in this sample is used to refine an earlier presentation of the paramagnetic (high-frequency) ²⁹Si resonance shifts in heavily-doped n-type silicon samples near the metal–nonmetal transition. The data show systematic decreases of the local magnetic fields with increasing temperature in the range 100–470 K for all samples in the carrier concentration range from 2×10¹⁸ cm⁻³ to 8×10¹⁹ cm⁻³. This trend is qualitatively similar to that previously observed for the two-orders of magnitude larger ³¹P impurity NMR resonance shifts in the same temperature and concentration ranges. The ²⁹Si and ³¹P resonance shifts are not related by a simple scaling factor, however, indicating that impurity and host nuclei are affected by different subsets of partially-localized extrinsic electrons at all temperatures.     

Diffusivity of a two-dimensional lattice fluid: CH4 adsorbed on MgO(100)

The diffusive motions of a 0.8 layer of CH₄ adsorbed on MgO(100) are measured at 72, 88 and 97 K by quasi-elastic neutron scattering. It is shown that at 72 K the methane film is solid and its molecules perform an isotropic rotational motion. At 88 and 97 K, the adsorbed layer is in a two-dimensional fluid state in which the molecules jump between equidistant (4.21 Å) lattice sites of the MgO surface. The mean residence time has been determined ( ∼ 1 × 10 ⁻¹⁰ s at 88 K and ∼ 4 × 10⁻¹¹ s at 97 K). The corresponding translational diffusion coefficients are ∼ 5 × 10⁻⁶ cm² s⁻¹ at 88 K and 12 × 10⁻⁶ cm² s⁻¹ at 97 K. The diffusivity of this lattice fluid is compared to that of the same molecules adsorbed on graphite (0001) previously reported. The reduced mobility observed in the case of CH₄/MgO(100) is related to the important depth of the potential wells on the MgO(100) surface.     

Photoluminescence of heavily doped n-InP

Photoluminescence and excitation spectra of weakly compensated n-type InP layers doped with tin in the density range from 3 × 10¹⁷ cm^-3 to 2 × 10¹⁹ cm^-3 are measured at T=2 K in order to get experimental informations about the influence of doping on important material parameters such as the band gap energy and the position of the quasi-Fermi level of electrons. The results derived from these investigations are compared with those obtained of relevant many-body theories to heavily doped semiconductors. Using RPA and Klauder's best (fifth) approximation the doping induced gap shrinkage of uncompensated n-InP is calculated. The comparison between theory and experiment yields the conclusion that for standard direct gap AIII-BV compounds such as InP and GaAs the compensation in principle expected has to be taken into the theoretical considerations. Moreover, we first present a “semianalytical” treatment of Klauder's multiple scattering approach which makes this theory easily applicable to other problems as for instance calculations of the luminescence line-shape of doped semiconductors.     

Stark shift of the CI 2479 Å spectral line of carbon

The Stark shift of the CI 2479 Å emission line of atomic carbon is measured in a broad range of electron densities between ~6 × 10¹⁶ and ~4 × 10¹⁸ cm^–3. It is established that the shift is linear and its value is significantly lower than that predicted by theory. The line shape is found to be dominated by the Stark effect at Т = 32 kK and electron concentration N _e ≈ 3.9 × 10¹⁸ cm^–3. The electron-impact and ion widths of this contour are in good agreement with the Grim data, while its total shift to longer wavelengths is found to be half that calculated theoretically.     

Photoluminescence associated with impurity clusters in phosphorous doped silicon

Photoluminescence measurements as a function of excitation level and temperature are presented for Si(P) containing 7.5×10¹⁷ P atomd/cm³. The luminescence in Si(P) for intermediate concentrations in the range from 1×10¹⁶ to 2×10¹⁸ cm^?3 is interpreted in terms of recombination of trapped carriers at clusters of impurities.     

Effect of the doping level on temperature bistability in a silicon wafer

The influence of the doping level on the effect of the temperature bistability in a silicon wafer upon radiative heat transfer between the wafer and the elements of the heating system is studied. Theoretical transfer characteristics are constructed for a silicon wafer doped with donor and acceptor impurities. These characteristics are compared with the transfer characteristics obtained during heating and cooling of wafers with the hole conduction (with dopant concentrations of 10¹⁵, 2 × 10¹⁶, and 3 × 10¹⁷ cm^?3) and electron conduction (with impurity concentrations of 10¹⁵ and 8 × 10¹⁸ cm^?3) in a thermal reactor of the rapid thermal annealing setup. It is found that the width and height of the hysteresis loop decrease with increasing dopant concentration and are almost independent of the type of conduction of the silicon wafer. The critical value of the impurity concentration of both types is 1.4 × 10¹⁷ cm^?3. For this concentration, the loop width vanishes, and the height corresponds to the minimal value of the temperature jump (～200 K). The mechanism of temperature bistability in the silicon wafer upon radiative heat transfer is discussed.     

ESR study of vanadyl ion in tripotassium citrate

ESR spectra of VO²⁺ doped tripotassium citrate are recorded at room temperature. The observed spectra are fitted to a spin Hamiltonian of orthorhombic symmetry with g_x = 2.001 ± 0.001, g_y = 1.997 ± 0.001, g_z = 1.945 ± 0.001, A_x = (49.0 ± 1) × 10⁻⁴ cm⁻¹, A_y = (66.8 ± 1) × 10⁻⁴ cm⁻¹ and A_z = (168.4 ± 1) × 10⁻⁴ cm⁻¹. The covalency and Fermi contact terms are evaluated and compared with those of other lattices.     

Photoluminescence observation of donor pairs in silicon

The asymmetric broadening with a tail on the lower energy side and the peak shift to lower energies are observed in the luminescence band due to bound excitons in silicon crystals which contain phosphorus impurities below the critical concentration for semiconductor-metal transition (8 × 10¹⁶ -3 × 10¹⁸ cm^-3). These behaviors are understood in terms of an exciton bound to a donor pair in silicon.     

3 MeV electron irradiation-induced defects in CuInSe2 thin films

3 MeV electron irradiation induced-defects in CuInSe₂ (CIS) thin films have been investigated. Both of the carrier concentration and Hall mobility were decreased as the electron fluence exceeded 1×10¹⁷ cm⁻². The carrier removal rate was estimated to be about 1 cm⁻¹. To evaluate electron irradiation-induced defect, the electrical properties of CIS thin films before and after irradiation were investigated between 80 and 300 K. From the temperature dependence of the carrier concentration in non-irradiated thin films, we obtained N_D=1.8×10¹⁷ cm⁻³, N_A=1.7×10¹⁶ cm⁻³ and E_D=18 meV from the SALS fitting to the experimental data on the basis of the charge balance equation. After irradiation, a new defect level was formed, and N_T0=1.4×10¹⁷ cm⁻³ and E_T=54 meV were also obtained from the same procedure. From the temperature dependence of Hall mobility, the ionized impurity density was discussed before and after the irradiation.