|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||L3, Study of Cause of Gm-Collapse for Higher Gate Voltages in N-Polar GaN HEMTs with Scaled GaN Channels
||Nidhi Nidhi, Oliver Bierwagen, Sansaptak Dasgupta, David Brown, Stacia Keller, James Speck, Umesh Mishra
|On-Site Speaker (Planned)
N-polar GaN/AlGaN HEMTs have been of interest to the nitrides community recently due to their several advantages over Ga-polar GaN-based HEMTs such as lower contact resistance, better electron confinement and enhancement mode operation. Currently, N–polar GaN HEMTs are being scaled to achieve X and Ka band performances. Scaling in N-face HEMTs, however involves scaling of GaN channel along with gate-length, in comparison to Ga-face where the barrier material is scaled instead of the channel. Scaled self-aligned HEMTs on N-face with regrown access regions reported by Nidhi et. al. at IEDM 2009 demonstrated significant reduction in access resistance. However, even though gm remained flat for large values of current due to no source choke in a self-aligned structure, it was observed that gm fell rapidly with higher gate biases even before the gate was forward biased. In this paper, this anomalous gm-collapse for higher gate voltages has been studied by using low temperature Hall and gated TLM measurements. It has been proposed that as the GaN channel thickness is scaled, application of higher gate biases shifts the centroid of the 2-dimensional electron-gas towards the GaN/SiNx-insulator interface, thereby causing mobility degradation which then causes the transconductance to collapse. It is proposed that the insertion of AlN interlayer above the GaN channel could help prevent the penetration of electron wavefunction into the SiNx due to the barrier created by the band-edge discontinuity and reverse polarization fields, and hence reduce the interface roughness and remote impurity scattering from the SiNx interface.