Are quantum semiconductor devices delivering?

As we are now half-way through the 1990s, it is timely to review the present semiconductor device scene and to establish the extent to which quantum effects, and especially the physics of low dimensional semiconductor structures established in the 1970s and 1980s, determine superior device performance. The following are examined: (i) various transistors as switches, amplifiers and oscillators, (ii) microwave diodes as sources and detectors: (iii) optical devices (sources, modulators and detectors), IR detectors and solar cells, and (iv) metrological devices as applications of low dimensional structures. The physics of heterojunctions, often on a 10 nm length scale, has been introduced into nearly every semiconductor device, and there have been some significant improvements to device performance in such primary figures of merit as efficiency, speed, noise etc. The secondary features, such as temperature stability, robustness, ease of manufacture, reliability,..., have all been improved. Heterojunction physics, often including its specifically quantum aspects, is now ubiquitous in semiconductor device operation. Wherever the trend is towards higher speed, efficiency or sensitivity in device operation, quantum effects are playing an increasingly important role. Those hoping for commercial devices with a radically new and intrinsically quantum mechanism for operation are largely disappointed. The new physics associated with one-dimensional and zero-dimensional structures, quantum interference, ballistic motion or Coulomb blockade is unlikely to lead to practical devices until these effects can be exhibited, if ever they can, as robust phenomena at 77 K if not at room temperature.