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The growth of InGaN alloys via Metal-Modulated Epitaxy has been investigated. Transient reflection high-energy electron diffraction intensities for several modulation schemes during the growth of 20% InGaN were analyzed, and signatures associated with the accumulation, consumption, and segregation of excess metal adlayers were identified. A model for shuttered, metal-rich growth of InGaN was then developed, and a mechanism for indium surface segregation was elucidated. It was found that indium surface segregation only occurs after a threshold of excess metal is accumulated, and a method of quantifying this indium surface segregation onset dose is presented. The onset dose of surface segregation was found to be indium-composition dependent and between 1 and 2 monolayers of excess metal. Below this surface threshold off excess metal, metal-rich growth can occur without indium surface segregation. Since at least 2 monolayers of excess metal will accumulate in the case of metal-rich, unshuttered growth of InGaN at the low temperatures required to suppress thermal and spinodal decomposition, this study reveals that some form of modulation must be employed to maintain this adlayer thickness. These theories were applied in the growth of InGaN with varying compositions using Metal-Modulated Epitaxy. Single-phase, high-quality InGaN films with compositions throughout the miscibility gap with root mean square roughnesses less than 0.8 nm were obtained, demonstrating the feasibility of shuttered, metal-rich InGaN growth.

The surface kinetics of InGaN alloys grown via metal-modulated epitaxy (MME) are explored in combination with transient reflection high-energy electron diffraction intensities. A method for monitoring and controlling indium segregation in situ is demonstrated. It is found that indium segregation is more accurately associated with the quantity of excess adsorbed metal, rather than the metal-rich growth regime in general. A modified form of MME is developed in which the excess metal dose is managed via shuttered growth, and high-quality InGaN films throughout the miscibility gap are grown.

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Thermal coupling of pulsed 10.6-μm laser radiation to aluminum and titanium targets was measured as a function of incident fluence, focal-spot size, and ambient pressure. Thermal coupling coefficients were measured with both calorimetric and fast-response surface-thermocouple techniques. Thermal coupling coefficients of over 0.3 were observed with the onset of a well-developed plasma at the target surface. The thermal coupling was observed to increase slightly with increasing irradiated spot size and to decrease monotonically with increasing laser fluence. Under conditions of low ambient pressure (∼0.5 Torr) the breakdown threshold was increased by a factor of 5 and at high incident fluences the thermal coupling was roughly a factor of 2 higher than at atmospheric pressure.

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InN, high indium content InGaN, and Mg-doped InGaN were grown by metal modulated epitaxy (MME). Transient reflection high-energy electron diffraction intensities were analyzed during the growth of InN and found to be similar to that previously reported for GaN and AlN. The x-ray diffraction rocking curve and background electron concentration of InN grown by MME were found to be respectable in comparison to recent reports in literature. InGaN alloys grown by MME were also investigated, and a method for detecting indium surface segregation was demonstrated. It was found that the shutter modulation scheme could be modified to prevent phase separation by indium surface segregation, and a range of single-phase InGaN samples with indium contents throughout the miscibility gap were grown. Using the discovered method of suppressing phase separation, several p-In x Ga 1 À x N samples were grown with indium contents from x ¼ 0 to 0.22. A maximum hole concentration of 2.4 Â 10 19 cm À3 was detected by Hall effect characterization, demonstrating feasibility of these p-InGaN layers for use in several device applications.