Publikationsserver der RWTH Aachen University
MOVPE and characterization of GaN-based structures on alternative substrates
Abstract
dc:descriptionIII-V-compound semiconductors based on the AlInGaN material system offer high chemical and thermal stability and bandgaps between 0.8 eV and 6.2 eV. They are suited for high frequency and high power devices as well as for light emitting diodes, which currently cover the ultra violet to green spectral region. In electronic devices the polarization properties are used to achieve a 2-dimensional electron gas (2DEG) with a high sheet carrier density at the hetero interface. A challenge for GaN-based epitaxy is the unavailability of commercial GaN-substrates for industrial use with an adequate price and therefore the growth is widely limited to heteroepitaxy, which is crystal growth on substrates of another material. Sapphire and silicon carbide (SiC) are the most commonly used substrates for GaN-based epitaxy. By using conventional growth techniques the grown layers exhibit dislocation densities in the range of 10E8 to 10E10 cm-2. Due to the limited layer quality of the deposited layers, which is not sufficiently good for the growth of laser diodes (LD) or high brightness LED and because of device degrading influences of the substrate material, the research on alternative substrates for GaN-based growth is important. This study involves growth experiments of GaN-based layer structures on silicon (Si), lithium aluminate (LiAlO2) and the composite substrate SiCOI. Substrate specific preparation and growth procedures were developed. Because of the different lattice constants and thermal expansion coefficients between GaN and the substrate materials and because of the high depositions temperatures (> 1000°C) complex interlayers are required to create a crossover from the substrate to the GaN layer and to prevent substrate/layer bowing and cracks developing in the epitaxial layers. Crystallographic, thermal and electronic properties of these materials were investigated and the developed layers were used as buffer layers for electronic and opto electronic devices. On Si AlN/GaN distributed Bragg reflectors (DBR), InGaN/GaN multiple quantum well (MQW) and AlGaN/GaN HEMT (high electron mobility transistor) were demonstrated. The transistor structures showed high power densities, which were comparable to industrially fabricated devices. As well as the reflection of a certain wavelength region, the DBR layers additionally showed positive influence on succeeding GaN top layer optical properties. For the first time laser emission of an optically pumped InGaN/GaN MQW on Si was demonstrated with low excitation density and a high operating temperature. GaN-based structures were deposited on LiAlO2 in the m-plane crystal orientation; that do not exhibit polarization mechanisms in growth direction. For the deposition of coalesced GaN films a seal-coating of the LiAlO2 surface was developed and finally LED structures were grown on these substrates. For the first time electroluminescence of LED structures on LiAlO2 was achieved. The growth on the composite substrate SiCOI was initiated with an HT AlN layer and it was demonstrated that SiCOI is comparable to a bulk SiC substrate for the GaN-based epitaxy. The developed and investigated layer structure served as buffer for the deposition of InGaN/GaN LED structures and AlGaN/GaN HEMT.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2006
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Dikme, Yilmaz
- Contributors dc:contributor
-
- Heuken, Michael
Subjects
dc:subject × 14Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- eng