Pa Tove

Charge collection in silicon detectors for strongly ionizing particles

Abstract Experimental results for the plasma time in a semiconductor detector are given for alpha-particles, 16 O ions and fission fragments. The plasma time t p is defined as the time needed to bring all carriers under the influence of the applied field. A simple theoretical model based on diffusion and space charge limited current erosion of the track is described and results in the expression t p = 1.32 × 10 −10 (n 1 E) 1 3 /F for a silicon detector where F is the electric field in the detector at the position of the track, n 1 is the linear carrier density in the track and E is the particle energy. This gives good agreement with the experimental data for tracks longer than ⋍ 15 μ m (alphas and 16 O ions of energies 5.3–8.8 MeV and 22–42 MeV, respectively). The shorter tracks of fission fragments (90 MeV from 252 Cf) give shorter t p values then predicted by the formula above. This is explained by transfer from cylindrical to spherical erosion geometry.

Plasma effects in semiconductor detectors

Abstract A phenomenological discussion of plasma effects in solid state detectors is given. For the case of weakly ionizing particles and/or high field strengths, it is shown that plasma effects are absent because of immediate polarizations of the tracks, and the simple concept of carrier transit time is valid. For strongly ionizing particles and weak fields, the effects of diffusion of the ionized column and of current erosion from its edge are discussed. Models are set up for the erosion (for planar and cylindrical geometries) in terms of space-charge limited currents from the plasma edge. This leads to expressions for the plasma time as a function of the detector field strength and the carrier density in the track. The results of the cylindrical model, which comply relatively well with experimental results for α-particles, give appreciably shorter times than calculations of ambipolar diffusion. The experimental results for fission tracks, which are short, agree better with threedimensional erosion geometry.

Pulse formation and transit time of charge carriers in semiconductor junction detectors

Abstract The formation and shape of the current pulse in semiconductor detectors is discussed theoretically. The transit time of released charge carriers and the resulting pulse rise time is calculated for n- and p-type junction detectors under the simplifying assumption of constant carrier mobilities and specific ionization loss and with neglection of eventual plasma effects. Expressions are given for the rise time and the results are also shown in nomogram form.

Transit time of charge carriers in the semiconductor ionization chamber

Abstract The transit time of charge carriers and the resulting pulse rise time are considered theoretically for a semiconductor particle detector, with particular reference to silicon detectors. Results are given in nomogram form for n- and p-type detectors, assuming constant mobility and specific ionization loss. The influence of various design factors is discussed, and the effect of non-constant mobility and ionization loss is calculated for typical cases.

IrSi1.75 a new semiconductor compound

Optical and Hall effect measurements on thin film layers of polycrystalline IrSi1.75 show that this material is a semiconductor. The band gap is approximately 1.2 eV. The films obtained saturated with silicon were p‐type with a charge carrier density of the order of 4×1017 cm−3.

A self consistent approach to IV-measurements on rectifying metal-semiconductor contacts

Abstract An experimental procedure is presented for the determination of the barrier height of metal-semiconductor contacts that avoids the use of the so called “ideality factor” n, common in the fit of experimental IV-data. We choose the commonly experienced case where the deviation of n from 1 is caused by a combination of recombination current contribution and the influence of series resistance. These effects are introduced into a computer fitting to the experimental forward IV data. We report on very good fitting of theory and experiment. Also, the discrepancy in the φB values determined by ordinary deduction from IV measurements and those obtained from photoelectric measurements practically vanishes if our procedure is used.

Complementary Si MESFET concept using silicon-on-sapphire technology

Complementary Si MESFETs (CMES) for integrated circuits using silicon-on-sapphire are described. Not only the gate, but also the source and drain of the n-transistors and p-transistors are Schottky junctions, using very high barrier heights for the gate and low barrier heights for source and drain. Only two Schottky metals are used: one, Ir or Pt, giving a high barrier on nSi, and hence low on pSi; the other, Er or Tb, showing the opposite behavior. The basic differences between MES and MOS are pointed out and design criteria for CMES inverters using normally-off type transistors are given.<<ETX>>

Calculation of charge distributions and minority-carrier injection ratio for high-barrier schottky diodes

Abstract Numerical calculations of charge distributions and injection ratios for high-barrier Schottky diodes are performed to extend the understanding of this type of phenomena under various conditions. The calculations are performed for two doping concentrations, 1014 and 1013 cm−3, in n-type silicon and for several barrier heights in the range 0.92-0.79 eV. Two sets of carrier lifetimes are used to give nominal diffusion lengths that are much larger than, or comparable with, the dimension of the structure. The boundary conditions at the barrier were those of the combined diffusion-emission model. The back contact was modeled as a perfect ohmic contact, or as a low-high junction. The results are compared with experiments involving the use of injecting Schottky rectifiers, capable of giving low forward-voltage drop and sustaining moderately-high reverse voltages.

Schottky rectifiers on silicon using high barriers

Abstract Schottky diodes are presently used for power rectification because of their low forward voltage drop. However, they have only been fabricated on relatively low resistivity and thin semiconductor layers. Hence the reverse breakdown voltages are low. To make diodes that stand higher reverse voltages, low doped material of sufficient thickness is necessary. Ordinary Schottky barriers do not inject minority carriers and the resistive voltage drop at high forward currents will be large, However, for high Schottky barriers ∼ 0.9eV, minority carriers are injected and the series resistance is decreased. In this paper we report results from one-dimensional numerical calculations as well as experimental results of high barrier Schottky diodes. We discuss the voltage drop at high forward currents for different substrate resistivity and thickness, as well as values of the high barrier.

DEVELOPMENT OF PARALLEL PLATE CHANNEL MULTIPLIERS FOR USE IN ELECTRON SPECTROSCOPY.

Abstract A simple method for designing parallel plate electron multipliers is described. Semiconducting and secondary emitting layers are deposited onto glassplates by rf-sputtering, and by placing two plates face to face with a separation of 0.6 mm a parallel plate multiplier is formed. The multipliers have a high gain (>10 9 ) and give output pulses with a very narrow pulse height distribution. The multipliers are used as detectors in electron spectrometers. The small dimensions imply that a large number of multipliers may be placed in the focal plane and used simultaneously.