MOCVD Nucleation And Growth Of Antimonide On Silicon And The Thermophotovoltaic Devices Simulaition

The III-V antimonide-based compound semiconductors have potential applications in optical and electronic devices, such as middle-infrared light emitters, photodetectors and HEMT. But the antimonide substrates are expensive and the producing process is difficult. However, the silicon has produced large size wafer with good thermal conductivity and mechanical strength and the price is low. Monolithic integration of silicon and antimonide compound semiconductor has attracted considerable attention, mainly for its applicability in developing multiple electronic and photonic devices on a single chip. The thermalphotovoltaic(TPV) cell is an important antimonide application field. It has broad application prospects such as the solar thermal photovoltaic power, hybrid power generation equipment, industrial waste heat recovery, etc.Aiming at the problems mentioned above, our work has been focused on the Ga Sb nucleation on the Si substrates, the In Ga Sb films grown by low pressure metalorganic chemical vapor deposition(LP-MOCVD) technique and the simulation of the Ga Sb/In Ga Sb single junction and tandem TPV cell structure.Firstly,the GaSb nucleation on Si substrate has been investigated. The growth temperature has great influence on the Ga Sb nucleation. With the growth temperature increasing, the number of Ga Sb nucleation and growth mode has changed. With the increasing of growth temperature, the number of Ga Sb nucleation on the Si substrate is increasing sharply while Ga Sb bonding to Si surface. So the Si surface is covered with the Ga Sb gradually. When the temperature is between 500 ℃ and 500 ℃, Ga Sb grows in SK mode with the strain releasing. As is in the stage of mass transportation, Ga Sb nucleation process is hardly affected by the growth temperature. In the high temperature(> 570 ℃), it increases the Ga Sb migration distance significantly on the surface. And the effect of vapor V/III molar ratio comes from that the Ga and Sb atoms on the surface have influence on the Ga Sb islands migration and coalescence. If the vapor V/III molar ratio is less than 1, the excessive Ga atoms would not only reduce the number of the nucleation of Ga Sb, but also enhance the nucleation migration and coalescence process. While the vapor V/III molar ratio is more than 1, the Sb atoms decrease the Ga Sb nucleation number and increase the island size. The effect of process parameters also has been analyzed. The process parameters include the growth time and annealing time. It is found that Ga Sb islands appear on the surface with the strain relaxed in SK mode in the initial stage. Then the islands were coarsening with the growth mode transited from SK to VW mode. Migration and Ostwald ripening were enhanced successively with the size of islands increased. In the annealing process, the coalescence process of migration and Ostwald ripening were obviously observed. In addition, the Sb atoms pre-deposition would decrease the number of nucleation and increase the islands size with Sb coherent behavior. And the Ga pre-deposition on the Si surface also reduce the Ga Sb nucleation number with the high surface mobility. Neither Ga nor Sb atoms pre-deposition have no obvious effect of Ga Sb nucleation. For the polar semiconductor is epitaxial on the non-polar semiconductor, Si(111) substrate is useful for Ga Sb nucleation which could reduce the antiphase domain.Secondly, the ternary InGaSb films were grown by LP-MOCVD. The properties and the growth process characteristics of the epitaxial layers were investigated. High growth temperatures could not only improve the surface morphology and crystalline quality, but also decrease the In components of the epitaxial layer. The mainly reason is that Ga atoms increase dramatically with the temperature increasing and Ga Sb has the priority to incorporate the epitaxial layer than In Sb. And the In gas-solid distribution coefficient decrease sharply with the temperature changing. Higher temperature is beneficial to increase the migration of atoms with the crystalline quality improving. The vapor V/III molar ratio impacts the In Ga Sb epitaxial layer crystalline quality and the surface morphology. The Sb or In droplets were emerged on the surface degrading surface morphology and crystallization quality which caused by the vapor V/III molar ratio too large or too small. So the vapor V/III molar ratio should be as far as possible close to stoichiometric ratio. The vapor Ga/III molar ratio impacts on the morphology of the epitaxial layer. For high In composition In Ga Sb film, it needs to increase the amount of Sb which is not only beneficial to more In incorporating into the epitaxial layer, but also reduce the In droplets to improve the crystalline quality of thin film. With the gradual increase of vapor Ga/III molar ratio, the In gas-solid distribution coefficient decreases gradually.Finally, the GaSb/GaInSb single and tandem TPV cells are simulated by the PC1 D. And the effect of devices parameters, such as the thickness and carrier concentration in the active region and window layer, on the output characteristics of the TPV cell is studied. In the tandem TPV cells, Si is chosen as window layer. This cell structure design could simplify the technological process and reduce the cost. The simulation of tandem TPV cells with optimized device parameters is carried out. In tandem TPV cell, Ga Sb homojunction is on the top and Ga In Sb homojunction is on the bottom. The effects of thickness and carrier concentration in each region on the cell output performance are analyzed in detail. In the top cell, output power of the tandem cell increases caused by emitter and base thickness increasing and it indicates that the emitter thickness has more influence on the output power. With the base carrier concentration increasing, the output power is decreased slightly. In the bottom cell, it reduced the output power of tandem cell gradually with both base and emitter thickness increasing. And increasing base and emitter carrier concentration decrease the output power of tandem cell. Simulated with the optimized parameters, the maximum output power in this tandem cell is 2.39W/cm2.