Heterojunction transistors are described consisting of n ZnSe epitaxially deposited on Ge base-collector junctions. The low-frequency common-emitter current gain is analyzed in terms of the injection efficiency and base transport factor. The injection efficiency is limited by interface recombination and capture-tunneling components in the emitter current, and the transport factor by low base lifetimes resulting from lattice and thermal mismatches involved with heterojunctions. Experimentally, the gain is constant at low injection levels and varies as a fractional power of the current at higher levels. The gain improves with decreased base widths and higher fields. Increasing the emitter resistivity reduces the capture-tunneling component in the emitter current, and increases the gain. Relatively small temperature dependence is observed, with β decreasing slightly at lower temperatures.

ZnSe-Ge heterojunction transistors

Heteroepitaxial films of silicon-on-sapphire were used to fabricate lateral bipolar n-p-n transistors. The devices have a common-base direct-current amplification factor of 0.9 and a maximum frequency of oscillation of 2.4 GHz. As a result of the vertical p-n-junction arrangement, small junction areas are possible, e.g. 1×10−6cm2, which yield depletion-layer capacitances of 0.02–0.05 pF.

Thin-film lateral bipolar transistor in silicon-on-sapphire structure

The unilateral gain defined by S. J. Mason, is a basic measure of the transfer activity of a two-port. It can be measured in a circuit made unilateral with lossless reciprocal elements. A general method of measurement is described, which in principle uses two reactances only; no transformers are required. The method has been realized in a coaxial-line circuit, and measurements have been made on a few transistors in the frequency range 100 to 900 Mc . The results confirm that the unilateral gain is indeed measured in this circuit. It is suggested that unilateral gain measurements are useful both for research into basic device performance and for the specification of power-amplifying ability.

The Measurement of Transistor Unilateral Gain

Cut-off frequency of a drift transistor

Certain conventionally defined characteristic frequencies of a drift transistor are related to each other, to the basic transistor parameters, and to minority carrier time constants, using the theory of the simple one-dimensional model The Frequencies are the common emitter and common base cut-off frequencies, and the frequency at which the magnitude of the common emitter short circuit current gain is unity; the minority carrier time constants are the effective lifetime, the average transit time, and the average time of stay in the base Several approximations for the frequency variation of the current gains are given, and used to find how junction capacitances and base resistance affect the measurement of the characteristic frequencies Finally the maximum frequency of oscillation is discussed, and the high-frequency figure of merit redefined in a way compatible with the conventional definition

J. M. Rollett

Papers

The Characteristic Frequencies of a Drift Transistor