Sb-doped Ge Research Articles

Vapor–liquid–solid growth and Sb doping of Ge nanowires from a liquid Au-Sb-Ge ternary alloy

Single-crystalline Sb-doped Ge nanowires (NWs) with excellent structural properties and uniform composition have been synthesized with high yield by vapor–liquid–solid (VLS) growth by low-temperature thermal evaporation from a mixture of Ge and Sb powders. During deposition, both the Ge and the Sb dopant became incorporated in the VLS seed nanoparticle. In situ annealing experiments during transmission electron microscopy establish that a liquid ternary Au-Sb-Ge alloy constitutes the active phase of the VLS seed drop at high temperatures, which governs the growth of the one-dimensional Ge NW and its doping by Sb.

Electronic and annealing properties of the E0.31 defect introduced during Ar plasma etching of germanium

Low energy (7 80 eV) Ar plasma etching has been successfully used to etch several semiconductors, including GaAs, GaP, and InP. We have studied the only prominent defect, E0.31, introduced in n-type Sbdoped Ge during this process by deep level transient spectroscopy (DLTS). The E0.31 defect has an energy level at 0.31 eV below the conduction band and an apparent capture cross-section of 1.4 10 14 cm 2 . The fact that no V–Sb defects and no interstitial-related defects were observed implies that the etch process did not introduce single vacancies or single interstitials. Instead it appears that higher order vacancy or interstitial clusters are introduced due to the large amount of energy deposited per unit length along the path of the Ar ions in the Ge. The E0.31 defect may therefore be related to one of these defects. DLTS depth profiling revealed the E0.31 concentration had a maximum (6 10 13 cm 3 ) close to the Ge surface and then it decreased more or less exponentially into the Ge. Finally, annealing at 2501C reduced the E0.31 concentration to below the DLTS detection limit.

Hydrogen ion drift in Sb-doped Ge Schottky diodes

Abstract Ion drift of negatively charged hydrogen was detected in Sb-doped Ge. The SbH pairs exhibit a dissociation energy of 1.36(6) eV. The dissociation energy of the dopant–ion pairs is determined by reverse bias annealing (RBA). Two different experimental techniques were applied: (1) CV-profiling of the passivated dopant profile after each RBA step, (2) detection of the capacitance time response of a reversed biased Schottky diode during RBA. The advantage of the later technique is the simplicity of the measurement. This technique also allows measurements on a shorter timescale, which is advantageous in n-type Ge, where strong retrapping of the dissociated hydrogen occurs.

Electrically active defects induced by hydrogen and helium implantations in Ge

Results of a study of electrically active defects induced in Sb-doped Ge crystals by implantations of hydrogen and helium ions (protons and alpha particles) with energies in the range from 500 keV to 1 MeV and doses in the range 1×10 10–1×10 14 cm −2 are presented in this work. Transformations of the defects upon post-implantation isochronal anneals in the temperature range 50–350 °C have also been studied. The results have been obtained by means of capacitance–voltage ( C– V) measurements and deep-level transient spectroscopy (DLTS). It was found from an analysis of DLTS spectra that low doses (<5×10 10 cm −2) of H and He ion implantations resulted in the introduction of damage similar to that observed after MeV electron irradiation. The Sb–vacancy complex was the dominant deep-level defect in the lightly implanted samples. After implantations with doses higher than 5×10 10 cm −2 peaks due to more complex defects were observed in the DLTS spectra. Implantations with heavy (⩾5×10 13 cm −2) doses of both H and He ions caused the formation of a sub-surface layer with a high (up to 1×10 17 cm −3) concentration of donors. These donors were eliminated by anneals at temperatures in the range 100–200 °C. Heat treatments of the heavy proton-implanted Ge samples in the temperature range 250–300 °C resulted in the formation of shallow hydrogen-related donors, the concentration of which was the highest in a region close to the projected depth of implanted protons. The maximum peak concentration of the H-related donors was higher than 1×10 15 cm −3 for a proton implantation dose of 1×10 14 cm −2.

Dynamic Threshold Switching Behavior of Ge[sub 2]Sb[sub 2]Te[sub 5] and Sb-doped Ge[sub 2]Sb[sub 2]Te[sub 5] Thin Films Using Scanning Electrical Nanoprobe

The dynamic oscillation in the current-time characteristics of Ge 2 Sb 2 Te 5 and Sb-doped Ge 2 Sb 2 Te 5 thin-film materials was investigated using a scanning electrical nanoprobe. The dynamic oscillation was attributed to the threshold switching of the amorphousphase Ge 2 Sb 2 Te 5 and doped Ge 2 Sb 2 Te 5 thin films. The microscopic mechanism of the threshold switching behavior was also studied. X-ray diffraction showed that the excess Sb improved the crystallization of Ge 2 Sb 2 Te 5 during postannealing at 300°C. Sb-doping also increased the threshold switching speed.

Enhanced Morphological Stability in Sb-Doped Ge

The axial heat processing (AHP) crystal growth technique was used to investigate the morphological stability of faceted solid/liquid (s/l) interfaces. Six Sb-doped Ge single crystals containing 2.3 × 10−2 to 2.3 × 10−1 at. pct Sb were grown at pulling rates of 10 to 20 mm/h. These include two bicrystals specifically designed to investigate the effect of slight misorientation on stability. Faceted growth with a kinetic supercooling on the order of 0.15 K was achieved, and a characteristic two-dimensional W instability boundary, an inverted crater in three dimensions, was observed. The crystals exhibited enhanced morphological stability over the predictions of the constitutional supercooling (CS) criterion and the Mullins and Sekerka (MS) stability criterion, with the highest stability in the center of the W. These results are examined with current analytical stability theories accounting for convection and kinetics. An alternate model is proposed based on anisotropic kinetics and the competition between lateral spreading on a faceted interface and the amplification rate of an interfacial perturbation.

Creating standard resistors based on germanium and silicon single crystals grown under microgravity conditions

Requirements on the creation of standard resistors (SRs), which are necessary for the calibration of microprobe complexes used for the diagnostics of electrical homogeneity of single crystal semiconductors, are considered. SR prototypes have been created based on Sb-doped Ge single crystals grown by float zone melting under microgravity conditions aboard the Photon series satellites, in which the inhomogeneity of the resistivity distribution does not exceed 1%. The main factors influencing the homogeneity of doping for Ge and Si crystals grown from melt under orbital flight conditions are formulated; methods for the optimization of this technological process are described.

Defects induced by irradiation with fast neutrons in n-type germanium

Electrically active defects induced in n-type Sb-doped Ge crystals by irradiation with fast neutrons have been studied by means of conventional deep level transient spectroscopy (DLTS). The neutron-irradiation-induced DLTS spectra are compared with those recorded after irradiations with 4 MeV electrons. The evolution of the neutron- and electron-radiation-induced defects upon 30-min isochronal annealing in the temperature range 100–300 °C has been investigated. Although the DLTS spectra from electron- and neutron-irradiated materials show some similarities and there are also significant differences. The neutron irradiation resulted in the appearance of a number of peaks related to electron and hole deep level traps in the DLTS spectra. In the upper half of the gap at least six electron traps were observed with the following activation energies for electron emission ( E n): 0.08, 0.12, 0.17, 0.22, 0.29 and 0.34 eV. Some of these traps were detected in the electron-irradiated samples. Particularly the trap with E n=0.34 eV was the dominant one after electron irradiation and was identified as the second acceptor level of the Sb–vacancy pair. In Ge:Sb samples irradiated with high fluences of neutrons the trap with E n=0.29 eV [ E(0.29)] was the dominant electron trap. It is argued that the E(0.29) trap is related mainly to the second acceptor level of Ge divacancy (V 2). It is suggested that upon annealing of neutron-irradiated samples at temperatures higher than 100 °C mobile divacancies and Sb–V pairs can interact with Sb atoms with the formation of Sb–V 2 and Sb 2–V complexes, which have acceptor levels in the lower half of the gap.

The antimony-vacancy defect in p-type germanium

Ge - n + p mesa diodes have been produced in 2-Ωcm single crystals using a molecular-beam epitaxy (MBE) process to grow the Sb-doped epitaxial Ge n+-top layer. The diodes are characterized by a leakage current at room temperature of 8×10−4A∕cm2 at a reverse bias of 3 V. The diodes have been used to study irradiation-induced defects in p-type Ge, in particular Sb-related defects, where Sb stems from in-diffusion during the MBE growth. Two lines in the deep level transient spectroscopy (DLTS) spectra are related to the presence of Sb. One of these lines originates from the single-acceptor state of the SbV pair with an enthalpy of ionization of ΔHp=(0.309±0.007)eV, the other from a state with an enthalpy of ionization of ΔHp=(0.095±0.006)eV, which is concluded to be the single donor-charge state of the SbV pair.

Electronic properties of antimony-vacancy complex in Ge crystals

Schottky barriers formed by depositing Au on n-type Ge have been used to study the antimony-vacancy complex (E center). Both hole and electron transitions have been observed because the formation of an inversion layer at the semiconductor surface enables minority carriers to be injected when the Schottky barrier is forward biased. It is argued that the E center in Ge has three charge states: double negative, single negative, and neutral. The free energy of electron ionization for the double acceptor level of the complex has been found to be ΔG(=/−)=0.294−4.2 kT (eV), where k is Boltzmann’s constant. Consequently, the position of the double acceptor level of the E center {E(=/−)=Ec−ΔG(=/−)} is temperature dependent. In moderately Sb-doped (NSb=1013–1015 cm−3) Ge crystals at equilibrium conditions half-occupancy of the double acceptor state of the Sb-V complex occurs when the Fermi level is at about Ec−0.20 eV. The single acceptor level of the E center is in the lower part of the band gap. The activation energy of hole emission from the E(−/0) level has been determined as 0.307 eV. The introduction of one Sb-V defect results in the removal of three free electrons in Sb-doped Ge. It is proposed that this is one of the main reasons for the fast free carrier removal and n→p conversion of the conductivity type in Ge:Sb upon electron- or gamma-irradiation at room temperature.

Far-infrared absorption in Sb-doped Ge epilayers near the metal–insulator transition

Epitaxial germanium layers doped near the metal–insulator transition were grown by liquid phase epitaxy from a Pb melt. Far-infrared absorption was measured between ∼20 cm−1 and 150 cm−1. Linear optical absorption coefficients were determined for Ge:Sb in the doping range of 9.0×1014 cm−3&amp;lt;ND&amp;lt;6.7×1016 cm−3. The peak absorption was found to increase linearly with dopant concentration as expected. The absorption at ∼50 cm−1 increased superlinearly with Sb concentration as a result of impurity banding. The optimal Sb concentration for extended far-infrared photoconductive response (λ&amp;gt;200 μm) in blocked impurity band detectors is discussed.

Preparation of Atomically Smooth Germanium Substrates for Infrared Spectroscopic and Scanning Probe Microscopic Characterization of Organic Monolayers

The suitability of antimony-doped germanium crystals for use as infrared attenuated total reflection wave guides and conducting substrates for scanning tunneling microscopic imaging of absorbed organic monolayers has been evaluated. We have used repetitive ion bombardment followed by resistive heating of a germanium crystal under ultrahigh vacuum conditions to produce large, atomically flat regions on a Ge(111) crystal face. Through the combined use of STM, Auger spectroscopy and low-energy electron diffraction, we have demonstrated that monolayer quantities of tellurium electrochemically deposited onto the Ge surface dramatically reduce the rate of surface oxidation and permit the use of germanium crystals as STM substrates in air. The first STM images acquired in air with Ge as the conductive substrate are reported. No degradation of IR spectral quality occurs when using the Te-covered, Sb-doped Ge crystals as ATR elements. These findings suggest that Te-coated, atomically flat, low-resistivity Ge substrates are suitable for both IR spectroscopic and STM imaging of organic monomolecular films.

The stress dependence of the change in sound velocity in Sb-doped Ge

We have measured the stress dependence of the change in sound velocity for Sb-doped Ge over a concentration N range 1.1*1016-1.3*1018 cm-3 and a temperature range 2.3-4.2 K. The revised density of states for N>1017 cm-3 has been derived from fitting to the temperature dependence of the change in sound velocity under zero stress. Qualitative agreement is obtained between the calculation of the stress dependence using the density of states derived and the experiment.

Convection and segregation during growth of Ge and InSb crystals by the submerged heater method

The submerged heater method was used to grow doped InSb and Ge crystals. The axial distribution of the dopants was found to be similar to space grown crystals. The ideal, diffusion-controlled steady-state segregation of Te-doped InSb was achieved for the first time in the terrestrial environment. One Sb-doped Ge single crystal was grown under steady-state conditions using a zone-leveling procedure.

Phonon conductivity of doped germanium under uniaxial stress in the

The relaxation-rate expressions for elastic, inelastic, and absorption phonon-electron processes in n-type germanium have been derived under [110] directional uniaxial tension. Using these expressions, the phonon conductivity of Sb-doped Ge under tension is evaluated and compared with the experimental results given by Keyes and Sladek. It is found that a slight increase of Bohr radii of the upper two levels of the donor ground states and decrease of shear deformation potential ${\mathit{E}}_{\mathit{u}}$ with stress can give better agreement with the experimental results. This work suggests that the theory of electron-phonon interaction is not a failure, as suspected by earlier workers.

The stress dependence of acoustic properties of heavily doped n-type Ge

The authors calculate the uniaxial stress dependence of the acoustic properties of heavily doped n-type Ge at low temperatures using Green function techniques. It is shown that the results are consistent with experiments of Sb-doped Ge made previously provided that Fermi levels lie in the impurity band. A brief discussion of the magnetic field dependence is also given.

MBE-grown Ge/GaAs heterojunction bipolar transistors operated at 300 K and 77 K with current gain of 45

The authors report the first fabrication of Ge/GaAs heterojunction bipolar transistors (HBTs) grown by molecular-beam epitaxy (MBE). Ge/GaAs HBTs have advantages of lower voltage operation, lower base resistance, and lower contact resistance over GaAs/AlGaAs HBTs, when applied to the high-speed digital circuits. Si-doped (n=1*10/sup 17/ cm/sup -3/, 3000 A) emitter layer, nondoped (p=1*10/sup 19/ cm/sup -3/, 1000 A) Ge base layer, and Sb-doped (n=3*10/sup 17/ cm/sup 3/, 5000 A) Ge collector layer are sequentially grown on GaAs

The change in the sound velocity in Sb-doped Ge

The authors have measured the change Delta v in the sound velocity in Sb-doped Ge over a concentration N range 3.1*1016-1.6*1018cm-3 and a temperature range 1.8-40 K. The stress dependence of Delta v has been also measured in a limited concentration range near the critical concentration Nc for the metal-nonmetal transition over a temperature range 2.3-4.2 K. The density of states for N>1017cm-3 has been derived from fitting to Delta v under the assumption that the electron-phonon coupling in the impurity band is identical with that in the conduction band. The stress dependence is qualitatively explained using the density of states obtained. The relaxation time in the sound attenuation near Nc is found to be sensitive to the stress. The metal-nonmetal transition in this system occurs in the impurity band.

The magnetic field dependence of the change in sound velocity in Sb-doped Ge

The authors have measured the magnetic field dependence of the change Delta upsilon in sound velocity in Sb-doped Ge over a concentration range 3.1*1016-4.6*1017 cm-3 and also of the sound attenuation constant for some samples. The aspects of the field dependence of Delta upsilon depend on the concentration and the directions of the field and the propagation of sound waves. The following results were found. The experiment on the sample with the lowest concentration gives evidence that the donor pairs contribute to Delta upsilon provided that the existing theories of the magnetic field dependence of the donor ground state are correct. The relaxation time in the sound attenuation is sensitive to the magnetic field near the metal-nonmetal transition; this suggests that the overlap of wavefunctions is important in relaxation processes.

The change in sound velocity due to donor pairs in Ge

The authors calculate the effects of the temperature, the magnetic field and the uniaxial stress of the sound velocity change Delta upsilon due to donor pairs in moderately Sb-doped Ge in the low-frequency limit. The nearly degenerate ground-state structure of an Sb donor is explicitly taken into account in calculating the eigenstate of a donor pair. The following results are found. The temperature and the stress dependences of Delta upsilon are qualitatively similar to those in the isolated donor system, although their magnitudes are smaller. The magnetic field (B) dependences for B//(111) and the (110) longitudinal mode are different; that is, Delta upsilon (B)= Delta upsilon (B)- Delta upsilon (B=0) becomes negative in the low-field region, while Delta upsilon (B) in the isolated donor system is always positive provided that existing theories of the magnetic field dependence of the donor ground state are correct. The scattering of high-frequency phonons by donor pairs is briefly discussed.