E.L. Heasell

Recombination beneath ohmic contacts and adjacent oxide covered regions

Abstract By modelling a contact as a Schottky barrier space-charge region it is possible to calculate the effective surface-recombination velocity which it displays. Such a model is of use in analysing the behaviour of thin emitter regions, and of contacts, or oxide covered regions in the extrinsic base of I 2 L vertical transistors. It is shown necessary to take account of both the doping and electric field dependence of the carrier mobility as well as the exact form of the potential at the boundary between the space-charge region and the substrate. The values of surface recombination velocity predicted by the model are in fair agreement with available data, and a tentative model for recombination beneath an oxide is proposed.

The properties of some metal-InSb surface barrier diodes

Abstract Metal-semiconductor surface barriers were formed by the vacuum evaporation of Au, Ag and Al onto n-type InSb. The current and capacitance curves of these devices were measured as a function of voltage at 77°K and analyzed in terms of existing theory. Surfaces etched in CP-4A followed by H100 and rinsed in 10−5 M Na2S formed inversion layers. Omission of the H100 step led to the formation of Schottky-type barriers.

A study of charge trapping in the Al-Al2O3-Si, MIS system

Abstract An experimental procedure, which maintains an almost constant electric field at the insulator-silicon interface, is used to study the trapping of electrons injected into the Aluminum-oxide gate insulator of a MISFET structure. A simple model, consisting of a finite number of traps, located at or adjacent to the insulator-silicon interface is consistent with the experimental observations. Additional experiments in which the insulator current is measured directly allow the capture parameter of these traps to be calculated.

The influence of illumination on the majority-carrier quasi-fermi-level in the Schottky-barrier diode

Abstract We present an analysis of the behaviour under illumination, of a Schottky-barrier diode. It is shown that significant changes in the position of the majority-carrier quasi-fermi level may occur in the space-charge region. Such changes enhance the forward current of the Schottky-diode, and so degrade the cell output. Further bias dependent effects may arise when bulk recombination in the neutral regions, or minority carrier leakage, across the n - n + episubstrate interface occurs. Recent published data on gold-silicon devices is used to compare predicted and experimental results. Good agreement in both qualitative and quantitative behaviour is found.

An analysis of the collection mechanisms in inversion layer solar cells

Abstract The characteristics of the surface-inversion-layer solar cell are analysed. The mechanisms of surface collection of the minority carrier, bulk generation and diffusion to the surface and lateral transport along the inversion channel are considered separately. The analysis illustrates the importance of the net inversion charge Q I , and its influence on the geometrical design of the cell.

Boundary conditions at p-n junctions

Abstract In recent correspondence and in earlier papers it has been shown that the use of the quasi-neutrality condition together with the Boltzmann relations at the boundaries of a p-n junction, leads to inconsistancies between the externally applied voltage and the change in potential across the space-charge region. We shall show that such boundary conditions lead to a consistent set of boundary values, when the potentials entering the analysis are correctly interpreted. The difference between the externally applied voltage and the decrease in electrostatic potential across the space- charge region may be interpreted as a purely electrostatic phenomenon, associated with the additional majority carriers present in the space charge region to establish quasi-neutrality.

Modelling of channel enhancement effects on the write characteristics of FAMOS devices

Abstract Physical modelling of floating-gate avalanche-injection MOS (FAMOS) devices in the program (write) mode is complicated by a feedback effect to the channel from the floating gate. The floating gate takes on a potential by virtue of capacitive coupling to the drain; this induces a channel near the source; the channel injects carriers into the depletion region near the drain and greatly enhances the avalanche multiplication current. This paper presents a simple method for taking account of this effect using empirical data, and thereby arriving at a first-order model of the FAMOS device. Measurements of drain current are subdivided into channel current and avalanche multiplication current, and a constant hot-carrier injection efficiency is assumed. The hot-carrier (avalanche) injection current is associated with a dielectric resistivity, whose dependence on the electric field in the oxide can be approximated by a simple exponential function. Model predictions for the write characteristics of FAMOS devices are in reasonable agreement with experiment.

A constant-current charging technique for the measurement of generation rates in MOS-capacitors

Abstract If a constant current is used to charge an MOS capacitor from accumulation into deep-depletion, then the space-charge region widens until the generation rate within that region exactly balances the charging current. At the same time the MOS capacitance is measured. From the known current and calculated space-charge width, the generation lifetime is immediately determined. Control of the charging current determines the depth of the sample studied. If the charging current is significantly larger than the generation current, then the time variation of the capacitive susceptance gives a direct plot of the cumulative impurity profile. The experimental circuit may be used without modification to perform a rapid “quasi-static” Q ϱ V G measurement, from which the surface potential, surface state density, flat-band voltage etc., may be found using Koomens method. The generation rate may be studied as a function of temperature to identify the activation energy of the centres responsible. A study of the forced return to accumulation identifies the location of the minority fermi-level.

Charge injection from a surface depletion region—The Al2O3-silicon system

Abstract Electron injection from a surface depletion region, over the surface barrier at an Al 2 O 3 -silicon interface is studied. The current passing over the barrier is measured by observing the rate of flat-band voltage shift as charge is trapped in the oxide. The data obtained is compared with the predictions of present models for charge injection. It is found that the so-called ‘lucky-electron’ model gives the most generally satisfactory agreement with the observations.

Recombinations via defects in degenerate semiconductors

Abstract It is shown that in degenerate materials, for a wide class of trap recombination models, it is possible to obtain the relevant capture rate equations by using a modified definition of the Shockley and Read trap parameters, n1, p1, etc. Thus we may obtain recombination rate expressions, in terms of quasi-Fermi levels, by using the solutions that are already in the literature for non-degenerate recombination models.