Charge carrier transport and electrical response by driving band gap modulation in semiconductors

Electrical responses and carrier transport dynamics in intrinsic bulk semiconductors are found when a variable gradient in a physical property or field causes a gradient in the band gap and, in turn, in the carrier concentrations. A variable carrier concentration profile leads to a dynamic carrier diffusion flow. The electrical responses depend on temperature and the difference between electron and hole mobilities. This novel effect is evaluated for both open-circuit and closed-circuit configurations. One example is a variable carrier concentration created by acoustically stimulated band gap modulation. A standing acoustic wave in the lattice produces a dynamic pressure-induced variable band gap modulation. Responses from an indium antimonide crystal in acoustic resonance with amplitude of 2.23 MPa (rms) are found to be in the ranges of 30-40 mA and 0.1-0.3 mV for closed and open circuit cases, respectively. At room temperature, quantum effects do not contribute significantly to the description of carrier behavior and transport, except for scattering. The effect can also be produced by perturbations other than pressure if the band gap depends on those perturbations. The electrical responses characteristic of these semiconductors can be used for developing new sensors or transducers to measure gradients, such as pressure gradient transducers.