Ulm, Univ., Diss., 2009.

GaN holds significant potential as a material for vertical p-n diodes, enabling the realization of devices with reverse breakdown voltages of 5 kV or higher. Carbon serves as the primary compensating dopant in the growth process, incorporated into GaN during metalorganic chemical vapor deposition (MOCVD) growth. The level of carbon incorporation depends on several factors, including growth rate, ammonia flow, temperature, pressure, and trimethylgallium (TMGa) flow. Through guided empirical modeling, it was demonstrated that the carbon incorporation in GaN growth could be predicted using a single parameter based on the ratio of ammonia flow to the growth rate. This model accurately predicts carbon concentrations ranging from 1x1017 to 5x1014 cm-3 while allowing for maximized growth rates. Other extrinsic dopants have either been reduced below the threshold of consideration or modeled using similar single-parameter relationships. By identifying the dominant extrinsic dopants and accounting for them, an intrinsic defect with a concentration of 2.2x1015 cm-3 was identified. By combining these relationships, growth conditions for n-GaN were optimized, resulting in electron concentrations as low as 1x1015 cm-3. Leveraging these techniques, p-n diodes were grown, achieving a reverse breakdown voltage as high as 3.1 kV. / Doctor of Philosophy / Power electronic devices based on vertical GaN have the potential to revolutionize applications such as electric vehicles, solar charging systems, and the smart grid. However, there are significant materials challenges that need to be addressed in order to realize these devices. They must be extremely pure and extremely thick. Unfortunately, the primary source of these materials also contains carbon, which can negatively impact purity. To overcome this challenge, an empirical model for the growth process has been developed. This model enables independent control over the carbon source and the removal of carbon, using a single parameter. By leveraging this model, it becomes possible to optimize the trade-off between high purity, high growth rates, and ideal electronic properties. Using these techniques, devices were grown with next-generation levels of performance at minimal time and cost.

<div>The work involves two new method implementation and application in the Quantum transport community for nano-scale electronic devices. </div><div><br></div><div>First method: Ab-initio Tight-Binding(TB)</div><div> </div><div>As the surfacing of novel 2D materials, layers can be stacked freely on top of each other bound by Van der Waals force with atomic precision. New devices created with unique characteristics will need the theoretical guidance. The empirical tight-binding method is known to have difficulty accurately representing Hamiltonian of the 2D materials. Maximally localized Wannier function(MLWF) constructed directly from ab-initio calculation is an efficient and accurate method for basis construction. Together with NEGF, device calculation can be conducted. The implementation of MLWF in NEMO5 and the application on 2D MOS structure to demystify interlayer coupling are addressed. </div><div> </div><div>Second method: Büttiker-probe Recombination/Generation(RG) method:</div><div><br></div><div>The non-equilibrium Green function (NEGF) method is capable of nanodevice performance predictions including coherent and incoherent effects. To treat incoherent scattering, carrier generation and recombination is computationally very expensive. In this work, the numerically efficient Büttiker-probe model is expanded to cover recombination and generation effects in addition to various incoherent scattering processes. The capability of the new method to predict nanodevices is exemplified with quantum well III-N light-emitting diodes and photo-detector. Comparison is made with the state of art drift-diffusion method. Agreements are found to justify the method and disagreements are identified attributing to quantum effects. </div><div><br></div><div>The two menthod are individually developed and utilized together to study BP/MoS2 interface. In this vertical 2D device, anti-ambipolar(AAP) IV curve has been identified experimentally with different explanation in the current literature. An atomistic simulation is performed with basis generated from density functional theory. Recombination process is included and is able to explain the experiment findings and to provide insights into 2D interface devices.</div><div><br></div><div> </div>