Carrier Transport Response and Behavior of Semiconductors Having a Gradational Energy Band Gap Due to Gradients in Pressure or Other Physical Properties



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This work investigates the physical behavior and transport of carriers in intrinsic bulk semiconductors with a variable carrier concentration gradient profile due to a variable physical property. If the energy band gap of a semiconductor depends on a physical property, a gradient in that physical property causes a gradational energy band gap in the semiconductor. A gradational energy band gap leads to a carrier density gradient and a carrier transport phenomenon. A semiclassical model is developed for the carrier transport, treating collisions and scatterings as quantum mechanical effects. The model is used to evaluate the transport for a bulk intrinsic indium antimonide crystal hosting an acoustic wave. Dynamic pressure effects and pressure-induced thermal effects cause two separate transport phenomena in the lattice. First, the conditions under which carriers can be treated as classical particles, and when quantum mechanical phenomena start to play a significant role are determined. It is shown how to include scatterings in the model using relaxation time and carrier mobility function under a pressure modulation. In the next step, a general semiclassical model for carrier transport is described. This model is based on a form of Boltzmann Transport Equation and scatterings are included in the formulation using a perturbation-dependent mobility function. Then, the model is used to predict the carrier transport due to a standing acoustic wave in a sample of indium antimonide. The diffusion current in closed-circuit configurations and the potential difference across the sample in open-circuit configurations are calculated. Lastly, pressure-induced thermal effects, related electrical responses, and dynamic pressure-induced thermoelectric effects are predicted. My results show that the peak of the pressure-induced diffusion current in the closed circuit is around a few tens of mA, and the peak of the electric voltage in the open circuit is in the range of 0.1 mV. The corresponding results for the pressure-induced thermal effects are in the range of 0.1 mA and a few of μV, respectively. The bulk temperature and ambient pressure affect the results. Changes in these parameters change the electrical responses around 0.3 percent per Kelvin and 10^(-11) percent per Pascal, respectively.



Semiconductor, gradational energy band gap, carrier transport