Abstract
The variation of the diffusion coefficent D(E) versus the electric field strength E, is determined at 300 K in n-type GaAs (N(D) = 3 x 10(-17) cm-3), using pulsed high-frequency noise measurements. D(E) is found to increase slightly at low field, then to decrease down to one tenth of its ohmic value near the threshold field. "Long" (greater-than-or-equal-to 4-mu-m) real n+-n-n+ Gunn diodes, with an arbitrary doping profile, can be modeled. Comparisons are made, and excellent agreement is found, between experimental and theoretical characteristics of two real diodes, with notch and with gradual doping profiles. The doping profile N(D)(x) is shown to have a considerable influence on the diode behavior, concerning the electric field profile as well as the noise characteristics. Using the impedance field method, the noise current is modeled and found to be very sensitive in the D(E) variation law, in particular in the range of 2.5-4 kV/cm. The agreement between the experimental noise and the computed noise of real diodes is found to be quite satisfactory when using D(E) determined in the present work, and important discrepancies occur when using other D(E) variations, both theoretical and experimental, found in the literature.