Measurement of minority hole zero-field diffusivity in n+-GaAs

Minority hole diffusivity, or equivalently the hole mobility, was measured in n⁺-GaAs with the zero-field time-of-flight technique. Devices for this study were fabricated on MBE grown films, and effects such as enhanced transport due to photon recycling and circuit effects were minimized with the device design. For a donor doping of 1.8 × 10¹⁸ cm⁻³, the minority hole diffusivity was found to be 5.8 cm²/s, which corresponds to a mobility of ~225 cm²/V.s; this is greater than the majority carrier mobility for comparably doped p-GaAs. This result for hole mobility has important implications for the design of devices such as pnp-HBT’s.