MOCVD Growth Of Self-organized Antimonide Quantum Dots And Simulation Of Thermophotovoltaic Devices

Recently, semiconductor quantum dots (QDs) with three-dimensional confinedstructure have been paid great attention for their unique electrical and opticalproperties. The density, size and uniformity of QDs have strong influence on theperformance of QDs devices. High quality quantum dots structure can be obtainedby controlling the growth parameters. A lot of work has been done on the preparationof Sb-based materials and device, but less has been done for its simulation. In thiswork, GaSb and InSb quantum dots structure are prepared by MOCVD, the effect ofgrowth parameters on quantum dot morphology is analyzed. On the other hand,Sb-based TPV device is simulated by Silvaco/Atlas software. the effects of thedevice parameters and the temperature are analyzed on the device characteristics.GaSb/GaAs quantum dots with high density and small size is preparaed byusing MOCVD technology. GaSb quantum dots with an average height of4.94nm,an average diameter of32.8nm and a density of2.45×1010cm-2are obtained byoptimizing growth parameter. The growth temperature, reaction pressure, gas phaseV/III, and growth process parameters are analyzed systematically for growth GaSbquantum dots. The thermodynamics theory and the property of organic source areemployed to explain the dependence of surface morphology of GaSb QDs on growthparameter. Whether the growth temperature is too high or too low will cause a largesize of quantum dot with the decreased density. The reaction pressure affects thequantum dot morphology by growth rate. With the increasing of V/III, the density ofquantum dots reaches a maximum and then drops down. The uniformity of quantumdots is affected by interruption time and loops. Then, InSb nanodots are prepared by MOCVD. The influence of growthparameters on the morphology of InSb nanodots is studied. Since the In source issolid, and the lattice mismatch between InSb and GaAs is14%. It is difficult toprepare InSb quantum dots with high density. InSb nanodots with small size andhigh density are growth at475C. The InSb nanodots are dome-like at high pressure.InSb nanodots with different growth time were verified in the effect of differentgrowth modes of quantum dot morphology.Finally, the GaSb/GaInAsSb single and tandem thermophotovoltaic (TPV) cellsare simulated using Silvaco/Atlas software. The effect of devices parameters and thetemperature on the output characteristics of the TPV device is studied. Thesimulation of tandem TPV cells with optimized device parameters is carried out. Forsingle TPV cells, P-type of GaInAsSb material is the main region for light absorption,its minority mobility is much larger than the majority mobility which improve theefficiency of collecting photon-generated carriers. The influence of thickness on thecharacteristic of the TPV cells is mainly on increasing the optical absorption areaand the junction width; the effect of doping concentration for the TPV cell is mainlyon the composite mechanism and less mobility and other aspects.The tandem TPV cells consist of the GaSb homojunction as the top cell andGaInAsSb homojunction as the bottom cell. Based on the simulation results, withemitter and base thickness of the top cell increasing, Pmaxof the tandem cellsdecreases. For bottom cell, Pmaxincreases rapidly as the base thickness of the bottomcell increases. For the effects of carrier concentration on Pmaxof the top cell and thebottom cell, with base carrier concentration increasing, Pmaxdeclines overall. In thetop cell, Pmaxis somewhat influenced by the emitter carrier concentration, but it isstrongly influenced by base carrier concentration. Pmaxdecreases rapidly with basecarrier concentration increasing. In the bottom cell, Pmaxdecrease rapidly with theincrease of emitter concentration. The simulation is carried out with deviceparameters fixed. Pmaxof the tandem TPV cell is almost2times that of thesingle-cells.Effects of radiator and working temperature on properties of TPV device are simulated. Along with the increase of the temperature of radiator, the optical powerdensity and the spectrum range increases, this will increase the Pmaxand Isc of TPVcells. The high working temperature reduces the Vocof TPV cells by carrierconcentration increasing.