Semiconductor structures and a method of forming semiconductor structures The avalanche breakdown characteristics, such as breakdown voltage and impact ionisation coefficient, of a semiconductor structure can be controlled by controlling the Brilluin-zone-averaged energy bandgap ( ) of the material forming the structure. Consequently, the avalanche breakdown characteristics of a device may be tailored independently of the bandgap Eg. The Brillouin-zone-averaged energy bandgap ( ) may be controlled by controlling the composition of the semiconductor used or by straining its lattice.

Method of forming semiconductor structure

The avalanche noise characteristics of InP/GaInAs (Ga/sub 0.47/In/sub 0.53/As) and InP/GaInAsP (Ga/sub 0.33/In/sub 0.67/As/sub 0.7/P/sub 0.3/) double drift region (DDR) heterostructure IMPact Avalanche Transit Time (IMPATTs) have been studied. The heterostructure IMPATT's in general are found to be less noisy compared to their homostructure counterparts and in particular the InP/GaInAs DDR is found to generate extremely low noise when the ternary layer width is properly selected. A noise measure of 7.7 dB has been observed at 190 GHz for a GaInAs layer width of 140 nm. Further, a study on the noise contribution from the individual space steps of the depletion layer due to individual noise sources in the generation region has revealed some interesting differences between those of homostructure and heterostructure diodes. Finally, a criterion for low-noise design is also suggested.

An extremely low noise heterojunction IMPATT

Semiconductor structures and a method of forming semiconductor structures The avalanche breakdown characteristics, such as breakdown voltage and impact ionisation coefficient, of a semiconductor structure can be controlled by controlling the Brillouin-zone-averaged energy bandgap ( ) of the material forming the structure Consequently, the avalanche breakdown characteristics of a device may be tailored independently of the bandgap Eg The Brillouin-zone-averaged energy bandgap ( ) may be controlled by controlling the composition of the semiconductor used or by straining its lattice

Method of forming a semiconductor structure

The potentialities of the material combinations InP/GaInAs and GaAs/GaInAs for single-drift-region heterojunction impact avalanche transit time diodes are investigated by computer simulation. The results indicate better device performance for the GaAs/GaInAs diodes than for the corresponding InP/GaInAs diodes. The reason for this is observed to be the large phase distortion caused by tunnelling of charge carriers in the InP/GaInAs diodes. The large phase distortion disturbs the phase relation between the radiofrequency voltage and current considerably for normal impact avalanche transit time mode operation, causing performance deterioration in the InP/GaInAs single-drift-region diodes.

https://iopscience.iop.org/article/10.1088/0022-3727/27/8/021/pdf

Computer-aided studies on the microwave characteristics of InP/GaInAs and GaAs/GaInAs heterostructure single-drift-region impact avalanche transit time diodes

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.

Are quantum semiconductor devices delivering

The authors' present the results of a study into the potential benefits of including heterostructures within single-drift impact avalanche transit-time (IMPATT) diodes. One particular heterostructure device, which exploits the change in saturated drift velocity in going from one material to another (the double-velocity avalanche transit-time (DOVATT) diode), is examined in detail using a series of GaAs/AlxGa1-xAs devices grown by molecular beam epitaxy. Contrary to claims in the literature, they conclude that there is little prospect for realizing high-performance DOVATT diodes using this materials system. The authors' note, however, that a novel InxGa1-xAs heterojunction technique to reduce series resistance appears promising and is deserving of further study.

N R Couch

Papers

Heterojunction impact avalanche transit-time diodes grown by molecular beam epitaxy