Breakdown of magnetic insulation in semiconductor plasmas

A theoretical analysis of the current response of strongly magnetized electrically biased photoconductors to short laser pulses, with emphasis on the breakdown of magnetic insulation, is presented. There are two regimes that result in breaking of the magnetic insulation during the "on" time of the pulse: (1) the collisionless regime, applicable to pulses with duration /spl tau//sub 0/<1//spl nu/, where /spl nu/ is the collision frequency, in which the magnetic insulation is broken by a polarization-like current induced by the fast rate of increase of the carriers, and (2) the collisional regime, applicable to pulses with /spl tau//sub 0/>1//spl nu/, where the magnetic insulation is broken at high carrier density due to the nonlinear dependence of the collision frequency on the carrier density. A simple experiment was performed which confirms the physics of the collisional regime. It is shown that the presence of the magnetic field can significantly reduce the response time of photoconductors. Response times shorter than a picosecond can be achieved in the collisionless regime.