Effect of optical radiation on millimeter‐wave characteristics and avalanche noise generation in double‐drift impatt diodes based on opto‐sensitive semiconductors

Abstract

RF properties and avalanche noise generation in opto-sensitive GaAs, InP, GaInAs, and GaInAsP double-drift INTRODUCTIONIn recent years, the optical control of microwave properties has become an active field of research due to its widespread application in modern communication systems. The tuning of IMPATT devices by conventional approaches is difficult, as it involves a critical design of a third terminal and its associated circuit for this purpose [1]. Earlier reports indicate [2] that the optimum frequency may undergo changes when the IMPATT diode is subjected to optical radiation, and thus by changing the intensity of incident optical radiation within the depletion zone of the diode, the oscillating frequency of IMPATT oscillator can be tuned.The mechanism of optical control in an IMPATT diode is realized by illuminating the diode through external ionizing radiation. The optical illumination varies the level of reverse saturation current, which alters the avalanche buildup of charge carriers and hence causes a further phase difference between the RF voltage and RF current. Without optical illumination, the saturation current entering into the depletion zone of the p-n junction is solely due to the thermally generated electron-hole pairs, which are subjected to avalanche multiplication in the high-field region of the p-n junction. The illumination of the IMPATT diode by photons having a photon energy greater than the band-gap energy of the semiconductor results in the generation of additional electron-hole pairs. The optically generated electron-hole pairs together with the thermally generated electron-hole pairs increase the level of the saturation current. The multiplication factor, which is an important parameter of the IMPATT diode operation, is directly related to the total saturation current. The multiplication factor (M) of the IMPATT diode, which is defined as the ratio of the total terminal current coming out (due to electron or hole) at the end of the p-n junction to the (electron or hole) saturation current entering the junction is taken to be infinite (10 6 for practical purposes) under normal IMPATT operating conditions. In the presence of optical illumination, the saturation current increases by orders of magnitude and thereby the multiplication factor decreases. For a sufficient proportion of optical component of generated saturation current, the multiplication factor becomes finite. This decrease in the carrier multiplication factor affects the normal characteristics of an IMPATT diode.The random process of impact ionization in a reverse bias p-n junction is responsible for the generation of avalanche noise in IMPATT diodes. Experimental and theoretical research work in the field of avalanche noise generation in IMPATTs has been carried out by several groups of workers in different parts of the world [3][4][5][6][7]. Their work on the estimation of avalanche noise in IMPATTs mostly considers integrated noise characteristics in solid-state RF oscillators and amplifiers. The intensity...

MM-wave performance and avalanche noise estimation of hexagonal SiC and GaN IMPATTs for D-band applications

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