Growth of non-polar and semi-polar gallium nitride with plasma assisted molecular beam epitaxy: Relatonships between film microstructure, reciprocal lattice and transport properties.

摘要

The group-III nitrides exhibit significant spontaneous and piezoelectric polarization parallel to the [0001] direction, which are manifested as sheet charges at heterointerfaces. While polarization can be used to engineer the band-structure of a device, internal electric fields generated by polarization discontinuities can also have a number of negative consequences for the performance and design of structures utilizing heterojunctions. The most direct route to polarization free group-III nitride devices is growth on either one of the "non-polar" prismatic faces of the crystal (m-plane (1010) or a-plane (1120)) where the [0001] direction lies in the plane of any heterointerfaces.; This dissertation focuses on the growth of non-polar and semi-polar GaN by MBE and on how the dominant feature of the defect structure of non-polar and semi-polar films, basal plane stacking faults, determines the properties of the reciprocal lattice and electrical transport of the films. The first part is a survey of the MBE growth of the two non-polar planes (10 10) and (1120) and three semi-polar planes (1011), (1013) and {lcub}11 22{rcub} investigated in this work. The relationship between basal plane stacking faults and broadening of the reciprocal lattice is discussed and measured with X-ray diffraction using a lateral-variant of the Williamson-Hall analysis. The electrical properties of m-plane films are investigated using Hall-effect and TLM measurements. Anisotropic mobilities were observed for both electrons and holes along with record p-type conductivities and hole concentrations. By comparison to both inversion-domain free c-plane films and stacking-fault-free free-standing m-plane GaN wafers it was determined that basal plane stacking faults were the source of both the enhanced p-type conductivity and the anisotropic carrier mobilities.; Finally, we propose a possible source of anisotropic mobilities and enhanced p-type conduction in faulted films is proposed. Basal plane stacking faults are treated as heterostructures of the wurtzite and zincblende polytypes of GaN. The band parameter and polarization differences between the polytypes result in large offsets in both the conduction and valence band edges at the stacking faults. Anisotropy results from scattering from the band-edge offsets and enhanced mobility from screening due to charge accumulation at these band edge offsets.