UC Santa Barbara

Post the commercialization and widespread use in light emitting diodes (LEDs), heterostructures of III-nitride semiconductors (GaN, AlN, InN, and BN) with their alloys, have shown immense promise in applications not limited to optoelectronics, but ranging from high power and high frequency electronics to plasmonics, sensor technology and quantum computing. While the superior properties of electrons and the two-dimensional electron gas (2DEG) have peaked a great deal of attention on this materials system, similar levels of advancements in p-type III-nitrides are required to tap into the complete benefits this semiconductor family can potentially provide. Like in most other wide-bandgap materials, the poor performance of p-type material in III-nitrides has led to only a few studies reported on p-channel III-nitride electronic devices. The use of p-type superlattice (SL) is valuable for III-nitride semiconductor-based p-channel Field effect transistors (pFETs) and LEDs because the polarization effects create a periodic oscillation of the energy bands, enhancing the ionization of the deep acceptors. Thus, the use of Mg-doped GaN/AlGaN SL is a pathway to get high hole concentration and mobility simultaneously, and pFETs engineered around a GaN/AlGaN SL have demonstrated record electrical performance.

The present study will systematically explore the electrical properties of epitaxially grown p-type Ga-polar and N-polar, modulation doped and uniformly doped GaN/AlGaN, and GaN/AlN/AlGaN superlattices (grown using the MOCVD growth technique). Following this, the discovery of a novel acceptor trap, proposed at 0.8 eV above the valence band of GaN, will be presented with simulations and experiments. The implications of this trap level, and its impact as the source of holes in dopant-deficient systems will be elucidated. This study will also explain in detail how charge balance is achieved in recent p-channel III-nitride electronic and optoelectronic devices. A detailed methodology will also be presented to predict and explain the mobility and high sheet concentration of holes in p-type III-nitride systems. p-type III-nitride material with record sheet resistance as low as 1.5 kΩ/sq will be shown. This work concludes with the development of highly doped p-GaN regrowth for use in p-channel III-nitride FETs with record normally-off performance.