Photorefractive phase shift induced by nonlinear electronic transport

Area of Science:

• Semiconductor Physics
• Photorefractive Materials
• Nonlinear Optics

Background:

• Photorefractive phase shifts are crucial for optical applications.
• Previous studies often assumed linear carrier transport.
• Understanding nonlinear transport is key to optimizing photorefractive devices.

Purpose of the Study:

• To investigate photorefractive phase shift generation under DC fields.
• To explore the role of nonlinear photocarrier velocity in phase shift dynamics.
• To analyze the impact of velocity saturation on space-charge field relaxation.

Main Methods:

• Theoretical analysis of photocarrier transport under DC fields.
• Modeling of photorefractive effects considering nonlinear velocity-field dependence.
• Investigation of velocity saturation and its influence on dielectric relaxation.

Main Results:

• Achieved photorefractive phase shifts as large as pi/2.
• Demonstrated that velocity saturation disables dielectric relaxation.
• Observed that nonlinear transport leads to saturated trap densities mimicking trap-limited behavior.
• Identified strong velocity saturation in direct-gap semiconductors due to hot-electron transport (Gunn effect).

Conclusions:

• Nonlinear photocarrier transport, particularly velocity saturation, significantly impacts photorefractive phase shifts.
• The space-charge field's inability to relax under these conditions leads to trap-limited behavior.
• Existing models of photorefractive trap-limited fields require reevaluation considering transport nonlinearity.