Electrical properties of polycrystalline GaInAs thin films

Polycrystalline GaxIn1 − xAs films with x ranging from 0 to 1 were deposited on glass substrates by molecular-beam deposition at 240 or 350 °C. Room temperature Hall-effect measurements showed that the GaxIn1 − xAs films deposited at either temperature exhibit high electron concentrations in the range of 1018 cm− 3 for x ≤ 0.21 while the electron concentration decreases with increasing Ga content for x ≥ 0.29 to be < 1015 cm− 3 at x = 0.64. Even at the low deposition temperature of 240 °C, the electron mobility remains > 400 cm2/(V s) at x ~ 0.2 and then decreases with Ga content to be ~ 40 cm2/(V s) at x = 0.64. Temperature-varying Hall-effect measurements in the range of 100–390 K revealed that both the electron concentration and mobility of the samples with x ≤ 0.21 are almost independent of the measurement temperature, while those of the samples with x ≥ 0.30 decrease with decreasing measurement temperature. The concentrations and ionization energies of donor levels were deduced from the temperature dependence of the electron concentration with the non-parabolicity of the conduction band taken into account. The temperature dependences of electron mobility in the samples with x ≥ 0.30 are well explained in terms of thermionic electron emission across the grain-boundary barriers assuming fluctuation in potential barrier height, while the almost temperature-independent high electron mobilities in the samples with x ≤ 0.21 are attributed to the absence of potential barrier at the grain boundaries.