Generation of terahertz electric oscillations by ballistic quantized holes with negative effective mass

The dispersion relation for the ground subband of quantized holes in a quantum well (QW) of zink-blende-like semiconductors contains an extensive section with negative effective mass (NEM). Under certain biases, stationary concentration distributions of the ballistic quantized holes in p⁺pp⁺-structures hold a self-organized region where holes with NEM predominate. The existence of such region causes a global instability of the entire stationary regime and the appearance of an oscillatory regime. We describe the dependence of the oscillatory regime on material and geometric parameters of the structure and consider factors that influence the oscillation frequency. The typical frequencies for 0.1 μm-structures are in the terahertz range (1-2 THz). The ballistic NEM-diodes have been classified as short, medium and long diodes depending on their oscillatory portrait. A new high-voltage region of oscillations that was not analytically predicted in early works is revealed in the so-called medium and long diodes. The region appears side by side with the stable stationary regime at high voltages. Switching between oscillatory and stationary regimes is studied. We also discuss the feasibility of ballistic transport of quantized holes in GaAs/AlAs p-QWs and substantiate a method of computer plotter of characteristics for a description of nonstationary processes.