In this work growth of cubic GaN in the selective area (SA) MOVPE process is simulated. The simulations are restricted to small pattern SA MOVPE growth. In this case the traditional MOVPE growth and the enhanced growth caused by surface diffusion are important growth factors. The lateral vapor phase diffusion is ignored while this process only has a small impact on the enhanced growth in the small pattern SA growth. The model is build for simulation of anisotropic growth. It has been shown that different type of anisotropic growth occurs when the mask pattern are orientated in different directions on the substrate. While the anisotropic growth is not well understood two different models are studied in this work. The simulation is restricted to the geometrical growth characteristics such as mask and crystal width, mask alignment and surface diffusion on the crystal. The reactor geometry, pressure and growth temperature are not investigated that closely and are only treated as constants in the model. The model used in this simulation gives good results for short time simulations for some certain cases. The model shows that the fill factor has a greater impact on the grown shapes than the individual mask and crystal width. But there are problems with the anisotropic and flux from mask modeling while some facets do not appear and the lateral growth along the mask show doubtful results. The model show good results in short time growth and predict some important characteristics in SA MOVPE.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 95-100).

Thesis (M.S.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Todd Weatherford, Ronald Pieper. Includes bibliographical references (p. 39-40). Also available online.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 158-170). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--School of Electrical and Computer Engineering, Georgia Institute of Technology, 2004. Directed by Nan M. Jokerst. / Vita. Includes bibliographical references (leaves 156-167).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 100-110). Available also in a digital version from Dissertation Abstracts.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 75-77).

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

GaN RF switches are widely used in today’s communication systems. With digital communications getting more and more popular nowadays, the need for improving the performance of involved RF switches is inevitable. Designing low ON-state resistance GaN switches are exceedingly important to improve the switch insertion loss, isolation and power loss. Moreover, considerations need to be taken into account to improve the switching speed of the involved GaN HEMTs. In this dissertation, a new GaN HEMT structure called “Tunnel MOS Heterostructure FET (TMOSHFET)” is introduced which has lower ON-state resistance and faster switching speed compared to conventional AlGaN/GaN HEMTs. In the switch ON process, the channel of this device is charged up by electron tunneling from a layer underneath the channel as opposed to typical AlGaN/GaN HEMTs in which electron injection from the source is charging up the channel. The tunneling nature of this process together with the shorter travel distance of electrons in TMOSHFET provide for a faster switching speed. In order to understand the tunneling mechanisms in TMOSHFET, the fabrication of AlGaN/GaN Schottky Barrier Diodes (SBDs) with various AlGaN thicknesses is demonstrated on Si (111) substrate. The impacts of SF6 dry etching on the trap density and trap state energy of AlGaN surface are investigated using the GP/w- w method. Various tunneling mechanisms at different biases are then characterized in samples and compared with each other. To improve the source and drain resistances in TMOSHFET, a model is generated to optimize the 2DEG density and electric field in AlGaN/GaN heterostructure based on Al mole fraction, AlGaN thickness and the thickness of SiN passivation layer and it is experimentally verified by non-contact Hall 2DEG density measurements. The spontaneous and piezoelectric polarizations together with strain relaxation have been implemented into the model, taking into account the annealing effects. From the experimental data on obtained parameters, the operation and device parameterization of the TMOSHFET is outlined and design considerations to improve the device R_(ON)-V_(BR) figure of merit are discussed.