MOVPE Growth of InxGa1−xN (x ∼ 0.4) and Fabrication of Homo-junction Solar Cells

The metal organic vapor phase epitaxy (MOVPE) growth of indium gallium nitride (InGaN) has been discussed in detail towards the fabrication of solar cell. The InGaN film with In contents up to 0.4 are successfully grown by controlling the fundamental growth parameters such as the precursor gas flow rates, temperature etc. The formation of metallic In originates from the higher value (0.74) of trimethylindium/(trimethylindium + triethylgallium) (TMI/(TMI + TEG)) molar ratio with low (4100) V/III weight molar ratio while the lower value (0.2) of TMI/(TMI + TEG) causes the phase separation. It is also necessary to control the growth rate and epitaxial film thickness to suppress the phase separation in the material. The crystalline quality of grown films is studied and it is found to be markedly deteriorated with increasing In content. The lattice parameters as well as the thermal expansion coefficient mismatch between GaN template and InGaN epi-layer are primarily considered as the reasons to deteriorate the film quality for higher In content. By using In0.16Ga0.84N films, an n+–p homo-junction structure is fabricated on 0.65 μm GaN template. For such a device, the response to the light illumination (AM 1.5) is observed with an open circuit voltage of 1.4 V and the short circuit current density of 0.25 mA/cm2. To improve the performance as well as increase solar photon capturing, the device is further fabricated on thick GaN template with higher In content. The In0.25Ga0.75N n+–p junction solar cell is found better performance with an open circuit voltage of 1.5 V and the short circuit current density of 0.5 mA/cm2. This is the InGaN p–n homo-junction solar cell with the highest In content ever reported by MOVPE.