<p>During the last decade, AlGaN High Electron Mobility Transistors (HEMTs) have been intensively studied because their fundamental electrical properties make them attractive for highpower microwave device applications. Despite much progress, AlGaN HEMTs are far from fully understood and judged by the number of published papers the understanding of advanced structures is even poorer. This work is an exploration of the electrical and structural properties of advanced HEMT structure containing AlN exclusionlayer and double heterojunctions. These small modifications had great impact on the electrical properties.</p><p>In this work, AlGaN HEMT structures grown on SiC substrates by a hot-wall MOCVD have been characterized for their properties using optical microscopy, scanning electron microscopy, transmission electron microscopy, capacitance/voltage, eddy-current resistivity, and by homebuilt epi-thickness mapping equipment.</p><p>A high electron mobility of 1700 [cm2/Vs] was achieved in an AlN exclusion-layer HEMT. A similar electron mobility of 1650 [cm2/Vs] was achieved in a combination of a double heterojunction and exclusion-layer structure. The samples had approximately the same electron mobility but with a great difference: the exclusion-layer version gave a sheet carrier density of 1.58*1013 [electrons/cm2] while the combination of double heterojunction and exclusion-layer gave 1.07*1013 [electrons/cm2]. A second 2DEG was observed in most structures, but not all, but was not stable with time.</p><p>The structures we grew during this work were also simulated using a one-dimensional Poisson-Schrödinger solver and the simulated electron densities were in fairly good agreement with the experimentally obtained. III-nitride materials, the CVD concept, and the onedimensional solver are shortly explained.</p>

During the last decade, AlGaN High Electron Mobility Transistors (HEMTs) have been intensively studied because their fundamental electrical properties make them attractive for highpower microwave device applications. Despite much progress, AlGaN HEMTs are far from fully understood and judged by the number of published papers the understanding of advanced structures is even poorer. This work is an exploration of the electrical and structural properties of advanced HEMT structure containing AlN exclusionlayer and double heterojunctions. These small modifications had great impact on the electrical properties. In this work, AlGaN HEMT structures grown on SiC substrates by a hot-wall MOCVD have been characterized for their properties using optical microscopy, scanning electron microscopy, transmission electron microscopy, capacitance/voltage, eddy-current resistivity, and by homebuilt epi-thickness mapping equipment. A high electron mobility of 1700 [cm2/Vs] was achieved in an AlN exclusion-layer HEMT. A similar electron mobility of 1650 [cm2/Vs] was achieved in a combination of a double heterojunction and exclusion-layer structure. The samples had approximately the same electron mobility but with a great difference: the exclusion-layer version gave a sheet carrier density of 1.58*1013 [electrons/cm2] while the combination of double heterojunction and exclusion-layer gave 1.07*1013 [electrons/cm2]. A second 2DEG was observed in most structures, but not all, but was not stable with time. The structures we grew during this work were also simulated using a one-dimensional Poisson-Schrödinger solver and the simulated electron densities were in fairly good agreement with the experimentally obtained. III-nitride materials, the CVD concept, and the onedimensional solver are shortly explained.

The thesis focuses on the gas flow profile optimization of a non-conventional injector in a hot-wall MOCVD system. The injector’s gas flow profile is simulated with CFD and demonstrates awell-behaved laminar flow with a parabolic profile. To ensure the theory is in coherence with the reality, a qualitative study with five thermocouples in a test graphite piece of the was performed. First the thesis will take you through an introduction of the semiconductor field to arrive in a problem formulation. Then you will read about the principles of MOCVD systems, fluid dynamics principles and thermocouple theory. The experiment’s way of approach is thendescribed through all steps from blue print to results. A discussion about the result and the conclusion will be read before the proposals of future work based on the thesis work. The laminar flow is confirmed according to the resulting data and the limitations of the system is set to two different cases depending on background temperature. At 1000 °C a laminar flow is strongly indicated to be obtained at position 3A, closest to the growth area, within the gas flow range of 25 SLM regardless of background pressure, except for 700 mBar indicating turbulent flow for 15 SLM an up. At 20 and 200 mBar the laminar flow limit is suggested by data to be even higher and reaching a value of 35 SLM. At 450 °C the data indicate a laminar flow up to 20 SLM at position 3A regardless of background pressure condition, except for 700 mBar where the data indicate a laminar flow at 35 and 40 SLM. 50 mBar strongly indicates a laminar flow profile up to a gas flow of 35 SLM. With a background pressure of 20 mBar, the data suggests a laminar flow profile up to at least 25 SLM. At 100 mBar the data indicates a laminar flow within the range of 30 SLM.