Dynamic and Steady‐State Injection of Electron‐Hole Plasma in p‐Type InSb

摘要

Potential measurements as a function of time and space show in detail the passage of an injected electron‐hole plasma front, and the eventual establishment of a nonequilibrium steady state in a long bar of p‐type InSb at 77°K. The front is preceded by a depletion layer which vanishes as plasma reaches the anode. Thereafter the current, with the voltage held constant, grows exponentially until just before the steady‐state plasma density is reached. These results are compared with a theory by Dean and by Ancker‐Johnson, Robbins, and Chang describing plasma injection into a semiconductor with deep traps. The measured front arrival time as a function of constant applied voltage agrees satisfactorily with Dean''s prediction. Four observations are at variance with his theory: the time constants of the exponential current growth are density‐dependent instead of being independent as predicted; the current at the front arrival is not a function of voltage as his theory states; the electric field behind the front is not proportional to the square root of distance; and the steady‐state injected current has a higher power dependence on voltage than the predicted square‐law dependence. The extended analysis accounts for all the observed growth time behavior, namely a growth time which is independent of steady‐state density at high and low densities, and which increases with density in the intermediate range. Also, a new theory of the steady‐state conduction characteristic, based on the density‐dependent plasma lifetime, reproduces quite well the measured conduction characteristics, I ∝ Vn with 2≪n≪8, until the interference of pinching, which causes a sub‐Ohmic conduction. In the nonequilibrium steady state the plasma density has a uniform spatial distribution within a factor of two over the central 80% of the sample length. The steady‐state den-nsity decreases monotonically from cathode to anode, or alternatively, a U‐shaped distribution is observed with high plasma densities occurring also at the anode, a characteristic which is attributed to copious hole injection. All the observed dynamic and steady‐state properties of double injection into p‐InSb are in good agreement with theory except for the constancy of the current magnitude at the front arrival and the form of the dependence of electric field on distance.