A. N. Lodygin

Silicon with an increased content of monoatomic sulfur centers: Sample fabrication and optical spectroscopy

The effect of the high-temperature heating (at 1340°C) of sulfur-doped silicon samples and their subsequent quenching is studied. The results of such a treatment are analyzed on the basis of Hall-effect data obtained in the temperature range T = 78–500 K. It is shown that the heating duration strongly affects the relative concentrations of different types of deep sulfur-related centers. At comparatively short heating durations of t = 2–10 min, the concentration of quasi-molecular S2 centers and SX complexes substantially decreases, whereas the density of monoatomic S1 centers grows. At the same time, the heating of a sample is accompanied by a monotonic decrease in the total concentration of electrically active sulfur over time. The results obtained make it possible to give recommendations concerning the optimal conditions for the fabrication of samples with a high concentration of S1 centers. The absorption spectra of the samples show that the method is promising for the observation of a number of quantum-optical effects involving deep S1 donors in silicon.

Modification of GaAs surface by low-current Townsend discharge

The influence of stationary spatially homogeneous Townsend discharge on the (1 0 0) surface of semi-insulating GaAs samples is studied. Samples exposed to both electrons and ions in a nitrogen discharge at a current density j = 60 µ Ac m −2 are studied by means of x-ray photoelectron spectroscopy, ellipsometry and atomic force microscopy. It is shown that an exposure to low-energy ions (<1 eV) changes the crystal structure of the semiconductor for a depth of up to 10–20 nm, although the stoichiometric composition does not change. The exposure to low-energy electrons (<10 eV) forms an oxide layer, which is 5–10 nm thick. Atomic force microscopy demonstrates that the change in the surface potential of the samples may exceed 100 mV, for both discharge polarities, while the surface roughness does not increase. (Some figures in this article are in colour only in the electronic version)

Control of the breakdown delay time in a micro-discharge system by small dc bias current

The possibility of making the breakdown delay time shorter in a micro-discharge (MD) system has been analysed. The delay time is controlled by passing through the system a low current from a dc voltage source. The delay time strongly depends on this bias current. In the presence of the control current, the time distribution of the breakdown probability shows two quite different characteristic times. This feature is due to the specific spontaneous dynamics of the MD system at low controlling current densities. The results obtained are important for determining the operation mode of high-speed MD devices.

Diffusion of interstitial magnesium in dislocation-free silicon

The diffusion of magnesium impurity in the temperature range T = 600–800°C in dislocation-free single-crystal silicon wafers of p-type conductivity is studied. The surface layer of the wafer doped with magnesium by the ion implantation technique serves as the diffusion source. Implantation is carried out at an ion energy of 150 keV at doses of 5 × 1014 and 2 × 1015 cm–2. The diffusion coefficient of interstitial magnesium donor centers (Di) is determined by measuring the depth of the p–n junction, which is formed in the sample due to annealing during the time t at a given T. As a result of the study, the dependence Di(T) is found for the first time. The data show that the diffusion process occurs mainly by the interstitial mechanism.

Dynamics of the Townsend discharge in argon

The characteristic time ϑ of the response of the Townsend discharge in argon is determined in short gaps at room and cryogenic (∼100 K) temperatures. In the structure used in experiments, one electrode is made of semi-insulating gallium arsenide, which ensures stabilization of the spatially homogeneous state of the discharge. The values of ϑ are obtained from the observed resonance frequency of the given structure. It is found that for both experimental temperatures, time ϑ in argon considerably exceeds the experimental values for a discharge in nitrogen in thin gaps, which were obtained earlier at room temperature. The results are of interest, in particular, for the development of high-speed IR image converters, in which the Townsend discharge in thin gaps is used.

High-temperature diffusion of magnesium in dislocation-free silicon

The diffusion doping of dislocation-free single-crystal silicon with magnesium is studied in the temperature range 1000–1200°C. The conventional sandwich method is used as the doping method. It is found that the diffusion coefficient of magnesium is described by a universal Arrhenius curve in the extended temperature range 600–1200°C, with data earlier obtained for the range 600–800°C taken into consideration. The relatively low activation energy of diffusion transport (1.83 eV) is indicative of the interstitial mechanism of impurity diffusion.

Townsend discharge in nitrogen at low temperatures: enhanced noise and instability due to electrode phenomena

The temperature dependence of the properties of the low-current Townsend discharge in nitrogen is studied. The experiments are carried out on a device with a high-resistivity semiconductor electrode in the temperature range 85–292 K at a current density not exceeding 25 μA cm−2. The discharge gap of the device is 0.85 mm, while the nitrogen density corresponds to the gas pressure Pa (49.5 Torr) at T = 292 K. The earlier increase found in the discharge sustaining voltage in time at a fixed current is quantitatively investigated for the cryogenic discharge. The relaxation is accompanied by transitions to new discharge states with an increased noise intensity. The characteristic time of the relaxation is hundreds of seconds. The effect is especially pronounced in the range of 100–150 K and is relatively weak at room temperature. The interpretation of the experimental data is based on the hypothesis that considers the formation of neutral aggregates of nitrogen in the form [(N2) n ]− in the discharge volume. The condensation of the clusters on the cathode leads to a change in its emission properties, which changes the properties of the discharge.

Doping of silicon with selenium by diffusion from the gas phase

Selenium-doped silicon single crystals are studied for the case of an impurity introduced by diffusion from the gas phase. Doping is performed in sealed quartz ampules at a temperature of 1240°C over the course of 240 h. The dependence of the concentration of the introduced deep donor centers of various types on the diffusant vapor pressure pSe is examined. It is found that samples with a concentration of atomic Se centers exceeding 1015 cm−3 can be obtained at comparatively low pSe (0.02–0.06 atm). In this case, the content of diatomic Se2 complexes is lower by an order of magnitude and more. The results obtained may be of interest for those who study nonlinear optical phenomena involving deep donor centers in silicon.

Silicon Doped with Sulfur as a Detector Material for High Speed Infrared Image Converters

The work aims at approaching the solution of the problem of developing sensitive silicon detectors for high speed IR imaging devices which are semiconductor – gas discharge systems. Among the requirements to detectors is their operation at the temperature which is somewhat higher than that of liquid nitrogen. To meet this requirement, a set of deep impurities is analyzed. It is emphasized that silicon doped with sulphur is a good choice to reach the aim. The doping of silicon with sulphur is done by the technique of high temperature diffusion. Data of the Hall measurements indicate the presence of large density of shallow donor levels in the material obtained. To compensate them, acceptors are introduced afterwards with using radiation doping techniques. Testing of the fabricated detectors in the converter setup shows that they provide imaging of IR fields of temperature T ~ 270 0C with the temporal resolution in the order of 3 µs.

Formation of S2 “quasi-molecules” in sulfur-doped silicon

The formation kinetics of the S2 complex in sulfur-doped silicon is studied. It is shown that the processes in which chalcogen “quasi-molecules” are formed in Si:S and Si:Se are similar. The difference is in the binding energy in a “quasi-molecule”: it is 1.5 times lower for S2, compared with the Se2 complex.