Gallium nitride semiconductor device issues

The advent of blue light emitting diodes (LEDs) based on wide band-gap nitride semi-conductor technology has spawn a hot bed of exciting research in material growth, characterization, device design and fabrication. As of today, most of the research has been centered on gallium nitride (GaN). However, other nitride alloys, such as aluminum nitride (AlN) and indium nitride (InN) are just as important because of their complete miscibility with GaN. This opens up the possibility of band-gap engineering of nitride heterostructure devices aimed towards high performance blue-uv light emitters and high frequency, high power and high temperature electronics.; Researchers have investigated numerous techniques for growing GaN and its alloys, such as molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), sputtering and pulsed laser deposition. All of these techniques have their respective strengths and weaknesses; however, MBE and MOCVD are the only two techniques thus far that have demonstrated working LEDs. Despite this initial success, many issues still need to be resolved in order for nitride technology to mature. Specifically, growth of high quality GaN is a big problem. The structural quality of as-grown GaN is still poor compared to other III-V semiconductors such as GaAs, as dislocation densities on the order of {dollar}10sp8{dollar}-10{dollar}sp{lcub}12{rcub}{dollar} cm{dollar}sp{lcub}-2{rcub}{dollar} are commonly observed. This can be attributed to the challenges of bulk GaN growth and to the lack of lattice-matched heteroepitaxial substrates.; This thesis focuses on MBE-grown GaN and its electrical properties, and some of the device technology issues associated with this material. How does this particular thesis contribute to the nitride community at large? First of all, we present electrical data of MBE-GaN. The quantification of electrical properties such as carrier concentration and mobility helps to provide valuable feedback to the growth process. By following the changes of these parameters with measurement temperature, impurity level locations and conduction mechanism can be inferred. When this information is coupled to optical and structural results, the growth optimization process can be initiated. Metallization is also discussed in this thesis. Its relevance lies in the need for both ohmic and rectifying contacts in GaN-based devices. We investigated both the materials and electrical characterization of these metal-semiconductor junctions. Finally, ion-implantation as a doping method is applied to MBE-GaN. The effects of annealing on carrier activation are studied and reported.