Large enhancement of the thermoelectric figure of merit in a ridged quantum well.

Recently, new quantum features have been observed and studied in the area of ridged quantum wells (RQWs). Periodic ridges on the surface of the quantum well layer impose additional boundary conditions on the electron wavefunction and reduce the quantum state density. As a result, the chemical potential of RQWs increases and becomes ridge-height-dependent. Here, we propose a system composed of RQWs and an additional layer on the top of the ridges forming a periodic series of p+-n+ junctions (or metal-n+ junctions). In such systems, a charge depletion region develops inside the ridges and the effective ridge height reduces, becoming a rather strong function of temperature T. Consequently, the T dependence of chemical potential is magnified and the Seebeck coefficient S increases. We investigate S in the system of semiconductor RQWs having abrupt p+-n+ junctions or metal-n+ junctions on the top of the ridges. Analysis made on the basis of Boltzmann transport equations shows a dramatic increase in S for both cases. At the same time, other transport coefficients remain unaffected by the junctions. Calculations show one order of magnitude increase in the thermoelectric figure of merit ZT relative to the bulk material.