J. Santana

Negative capacitance effects in semiconductor diodes

Abstract Negative capacitances have been observed and reported in several physical systems. These are discussed briefly. For metal-semiconductor or P+-N diodes with high resistivity, or semi-insulating material the mechanism is shown to be due to the relaxation-like nature of the material and is to be expected from established theory.

GaAs solid state detectors for particle physics

Abstract We report on progress with Schottky diode and p-i-n diode GaAs detectors for minimum ionising particles. The radiation hardness and potential speed of simple diodes is shown to be more than competitive with silicon detector. A discussion is given of the present understanding of the charge transport mechanism in the detectors since it influences their charge collection efficiency. Early results from microstrip detectors are also described.

Semiconductor detectors for use in high radiation damage environments — Semi-insulating GaAs or silicon?

Abstract There is a need for high-resolution solid-state tracking detectors for use in high radiation, long-life experiments where there can be considerable degradation in their electrical performance. A discussion is given of the relative merits of GaAs and silicon in the context of the underlying semiconductor device physics. Although the relative performance, in terms of the charge collection efficiency at the end of life, depends on the details of the type and amount of damage produced, it is shown that the qualitative electrical behaviour is predictable using relaxation semiconductor theory. Experimentally, diodes of semi-insulating GaAs and irradiated silicon have similar qualitative performance. Suggestions are given as to how the performance may be improved.

Semi-insulating GaAs as a relaxation semiconductor

It is shown that semi-insulating GaAs diodes exhibit all the qualitative electrical properties expected from a relaxation semiconductor. The degree of ideality increases after irradiation by neutrons for liquid encapsulated Czochralski and liquid phase epitaxy (LPE) material although LPE material is almost lifetimelike directly from manufacture. Experimental results are shown for current–voltage and capacitance–voltage frequency over a range of temperatures for samples in the low- and high-space charge limit conditions. The implications for commercial GaAs and other compound semiconductor devices are discussed.

NUMERICAL ANALYSIS OF CHARGE TRANSPORT IN SEMI-INSULATING GAAS WITH TWO CONTACTS

The dc, steady state charge transport in 200‐μm‐thick semi‐insulating GaAs samples with two large whole area metal contacts is calculated numerically. The material is assumed to have shallow donors and an excess of deep acceptors. The distributions of the space charge density and of electron and hole conductivities are calculated for different electron and hole‐supplying contacts with different bias voltages. It is found that the contact which injects majority carriers into the semiconductor due to the voltage bias determines the distribution of the space charge density in a greater volume of the sample than the other contact. Consequently, this contact is decisive for the space distribution of the electric field and the shape of the current–voltage (I–V) characteristic. Comparison is made with experimental observations of the I–V characteristics of one of our detector of particles.

Charge transport properties of undoped SI LEC GaAs solid-state detectors

Abstract The GaAs detectors for minimum ionizing particles fabricated with commercial undoped SI GaAs show good quality as minimum ionizing particle detectors. A discussion is given of the present understanding of the charge transport mechanism in the detectors since it influences their charge collection efficiency.

Gallium arsenide microstrip detectors for charged particles

Microstrip detectors have been constructed from gallium arsenide (GaAs) wafers made from undoped LEC (liquid-encapsulated Czochralski) semi-insulating substrate material. Tests were performed using minimum ionising particles to ascertain their properties as charged particle detectors. The results show that the devices work wellm, with good signal-to-noise ratio (typically 7). The effects of gamma ray and neutron irradiation have been studied and shown to be small up to levels exceeding 20 Mrad and 1014 n/cm2, respectively.

Ohmic I–V characteristics in semi-insulating semiconductor diodes

Abstract The contact made between a semi-insulating semiconductor and a metal (Schottky diode) or a low resistance semiconductor (bipolar diode) often gives an Ohmic I–V characteristic. This can be explained by standard relaxation semiconductor theory without the need for any special assumptions and the electrical properties can be predicted. These include the measured material resistivity, the temperature coefficient, the departures from the Ohmic character and possible negative capacitance effects. There are technological implications for devices using semi-insulating materials, such as MESFETs.

Gallium arsenide charged particle detectors; trapping effects

The progress on the development of gallium arsenide particle detectors is reviewed. The limitation to the performance is the presence of traps. Studies of the trap properties using α particle DLTS measurements and C-V measurements are described.

Gallium arsenide detectors for minimum ionizing particles

Abstract Progress on the development of GaAs solid state detectors is presented. 80% charge collection efficiency has been achieved, and double sided detectors with metal rectifying contacts have been tested. Measurements of capacitance and tests with SEM are giving more information on the behaviour of these devices.