L. M. Portsel

Speed properties of a semiconductor-discharge gap IR image converter studied with a streak camera system

Under certain experimental conditions a semiconductor‐discharge gap structure can be used as detector for spatiotemporal resolved measurements on IR radiation. With a streak camera system and a semiconductor laser diode (λ=1.3 μm), we investigate experimentally the speed properties of this kind of converter. The experimental results are compared with the predictions of a simple theoretical model.

HIGH SPEED CONVERSION OF INFRARED IMAGES WITH A PLANAR GAS DISCHARGE SYSTEM

The speed of conversion of infrared (IR) images by a planar semiconductor gas discharge system into the visible range has been investigated. Argon or nitrogen are used in the discharge gap having an electrode distance of 100 μm. Using pulse radiation from an IR laser to excite the system, we have shown that the characteristic response time of the device with the cryogenic discharge in the gap can lie in the submicrosecond range. This characteristic of the system can be applied for a fast IR imaging at a rate higher than 106 frame/s.

Glow dynamics in a semiconductor-gas discharge image converter

Transient phenomena which accompany the breakdown of gas in a semiconductor-gas discharge (SGD) system with 100 μm interelectrode distance have been studied experimentally and with numerical calculations. This system serves as the basis for an image converter operating in the infrared (IR) spectral region. The experiments are done for a cryogenic discharge in helium at a temperature close to that of liquid nitrogen. Depending on specific experimental conditions, oscillatory or aperiodic modes approaching to the steady-state current are observed after breakdown has been induced by a step-like voltage pulse. Numerical calculations of transient phenomena were performed for experimental conditions within the framework of the Townsend model, taking into account direct ionization, Penning ionization and secondary emission of electrons from the cathode. The main features of discharge kinetics obtained are in accordance with experimental data. At the same time, with the steady-state discharge current density vary...

An effective infrared-visible conversion technique for remote quantitative measurements of thermal fields

In this paper we study the applicability of a semiconductor gas discharge (SGD-) structure with a cryogenic discharge in neon for measuring spatially extended temperature distributions of heated bodies. The IR radiation from a heated body excites the photosensitive semiconductor cathode of the device thus controlling the current density and the visible light emission from the gas discharge layer. The infrared radiation distribution emitted by the heated body can be found from the visible discharge glow in the gas layer. Present experimental investigations show that the lower temperature limit of this technique is about 400 K while the spatial resolution is in the order of 50 to 100 μm.

Gas-phase doping of silicon with sulfur

The high-temperature gas-phase doping of silicon with sulfur has been studied at various sulfur vapor pressures. It is shown that the content of one- and two-atom sulfur-related deep donors in the semiconductor can be quantitatively controlled by varying the diffusant vapor pressure.

Townsend-like discharge: the suppression of instabilities by a semiconductor electrode

This study compares the stability of a gas discharge in a planar system that has metallic electrodes with a system that has an electrode made of high-resistivity semiconductor material. The discharge gap was filled with nitrogen. For these measurements, the devices were fed with a current up to ~1 mA and a constant (dc) voltage over the gap d, which ranged from 0.08 to 10 mm, at the minimum of the Paschen curve (pd ≈ 1 Torr cm). For the system with metallic electrodes, no stable state was observed for the entire range of the parameters studied; the discharge occurred in the form of relaxation oscillations where the period decreased as the current increased. The behaviour of the device changed dramatically when the metallic electrode was replaced by a semiconductor electrode. Relaxation oscillations in the current were observed for the semiconductor electrode for d ≥ 5 mm as well, but a stability domain appeared for smaller values of d that expanded as d decreased. At d < 0.2 mm, the discharge was stable for the range of current values used in this study. A strong level of excess noise was observed for this mode of operation. It is supposed that this discharge mode corresponds to the existence of a large number of oscillating microdischarges in the device. As the current increases, their interaction can lead to synchronization of the discharge dynamics in different parts of the planar structure, that is, a loss of stability in the macroscopic steady state. The results may be of interest in the development of low-power microdischarge devices where a stable homogeneous discharge is required.

Noise properties of a high-speed semiconductor-gas-discharge infrared imager

The imager consists of a planar semiconductor-gas discharge (SGD) cell allowing the ultra fast IR-to-visible conversion with response time on the microsecond scale. The semiconductor wafer is made of Si:Zn providing the spectral range of 1.1 - 3.5 micrometers . The 100 micrometers discharge gap is filled with Ar under the pressure of 100 hPa. The cell is cooled down approximately to 90 K. Among studied properties are noise, both in time and space domains, detectivity, noise equivalent irradiance and, when applying the imager in a thermal imaging system, noise equivalent temperature difference (NETD). Investigations of the spatial noise and NETD have been carried out by using a low-noise CCD camera capturing output images of the SGD cell. For measuring the temporal noise, a low-noise photomultiplier is used to detect gas discharge radiation from the area of about one resolved pixel. The own noise of the SGD cell is found by comparing signal-noise dependencies obtained at acquiring outgoing light of the cell, on the one hand, with those at observing a thermal radiation source with well describable photon noise, on the other hand. The results indicate that the imager has surprisingly low noise which is very close to the photon-noise limit.

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.