The Transient Study On Gallium Arsenide Photoconductive Switches

THE TRANSIENT STUDY ON GALLIUM ARSENIDEPHOTOCONDUCTIVE SWITCHES Speciality: Microelectronics Candidate: (signature) Supervisor: (signature)As far as the power and band width of electronic pulses are concerned, optically controlled Photoconductive Semiconductor Switches (PCSS's) are the most effective microwave radiant sources. Due to the intrinsic characteristics of the GaAs material, Semi-insulating (SI) GaAs PCSS's have more obvious advantages in the performance of both high power and ultra-fast switching than those PCSS's made of other materials. The GaAs PCSS's can take on the particular phenomenon of Lock-on effect when the thresholds of activating optical energy and bias field, which the devices demand, are meted simultaneously. Accordingly, the great importance was attached to the device research and application of the GaAs PCSS's. Up to the present, there are no reliable theories that can correctly account for the observed transient characteristics produced by the Lock-on effect.The electronic pulse waveform of linear, non-linear and the critically transiting switching modes outputted from the SI-GaAs PCSS's was observed and measured. Especially, we repeatedly measured the bias field thresholds and Lock-on field of the critical transiting mode from the linear to non-linear state. Based on the transferred-electron theory of the III-V compound semiconductor and the research on the Lock-on effect of the SI-GaAs PCSS's, this paper proposes the monopole charge domain model similar to the Guun or high-field domain to explain the peculiar switching phenomena occurring in the Lock-on mode theoretically. Owing to the field enhancement in the domain, the avalanching gain and recombination radiation are induced and the switches occur the special phenomenon of the Lock-on effect. When the triggering light goes, the avalanche impact ionization and recombination radiation in the domain result in the formation of the carriers' conductive channel in the body of the devices and control the current of the Lock-on switching. Based on the theory mode, the delay time between the beginning of optical illumination and the onset of Lock-on switching was calculated, and the transiting speed of electrons, the traversing velocity of the current filament, was obtained as well. The calculated results matched well the experimental results.Taking advantage of the ultra-fast response characteristics of the devices, SI-GaAs PCSS's are successfully applied to the broadening test of nanosecond laser pulses. Our tests show that the switches could be used in the ultra-fast photoelectric response and the photoelectric feedback net.