III-V nitride semiconductors have attracted a lot of interest for their applications in optoelectronic and high power devices. However the highly resistive p-type layers of nitrides have limited the performance of bipolar devices. Polarization charges present in nitride heterojunctions can be engineered to enhance the performance of different devices and introduce novel material physics not present in other semiconductors.
Regions of 2- and 3-dimensional mobile carriers can be produced with the aid of polarization charges in graded AlGaN structures. Such impurity-free electron concentrations have been demonstrated experimentally. Polarization-enhanced hole concentrations are theoretically and experimentally studied in this work. Bandgap engineering of polarization-induced doping in III-V nitrides is demonstrated by Molecular Beam Epitaxy. Applications of these polarization-enhanced layers in working p-n junction diodes is achieved.
Polarization charges can also utilized to enhanced the properties of other devices. p-type conductivity in AlN/GaN superlattice structures is increased due to field-assisted acceptor ionization. Improved p-type conductivity as compared to conventional bulk doped GaN structures is achieved, and insertion into a p-n junction allows vertical conductivity.
Demonstration of the nitride-based backward diodes is also achieved by utilizing the high polarization-induced electric fields. Interband tunneling current is observed in GaN-AlN-GaN p-n junctions under reverse bias. Application of these backward diodes as a zero bias RF detector is demonstrated.