Noise Properties of Very Short Gallium-Arsenide Devices.
Noise properties of n('+) n('-) n('+), p('+) p(' -) p('+), and p('+) n('-) p('+) GaAs structures are investigated. The thickness of the n-type devices are .24(mu)m, .4(mu)m, and 2.0(mu)m while the p('+) n('-) p('+) and p('+) p(' -) p('+) have a thickness of .4(mu)m. These very short devices are of interest since they are useful tools to investigate fundamental phenomena such as ballistic transport and l/f noise. Current-voltage measurements and low frequency noise measurements at room temperature for every device previously mentioned are presented. Comparison between the various levels of l/f noise in the n-type devices leads to the conclusion that mobility fluctuations are responsible for noise in these devices, since in the shorter devices (.24(mu)m and .4(mu)m), the noise level is low. This suggests some carriers have a near-ballistic transport. The high level of low frequency noise in the p('+) n('-) p('+) device suggests the possibility of noise due to traps in this device. The noise at high frequency and at high electric fields is further investigated on the 1.1(mu)m n-type device. A step-up transformer is designed to bring the noise of the device to a level above that of the radio frequency preamplifier. The noise at high electric fields can be explained in terms of velocity fluctuations due to intervalley scattering. The electron drift velocity v(E), and the electron diffusion coefficient D(E) obtained from the measurements by the numerical deconvolution of the I-V characteristic and the noise spectral density, are compared to those obtained by Monte Carlo simulation techniques.
- Pub Date:
- December 1985
- Engineering: Electronics and Electrical; Physics: Condensed Matter