Investigation of the impact of impurities on the properties of nitride semiconductors grown by RPECVD

Abstract

Progress toward the improvement of optical emission from InGaN optical active region devices is made through a combination of the tailoring of p-type gallium nitride growth recipes and bandstructure calculations on a graded InN-GaN bandstructure that provides insight into the causes of anomalous electroluminescence observations. Using a 7nm thick amorphous aluminum nitride buffer layer, the quality of certain thin film, ~150nm thick GaN growths performed at 550C at 1360mTorr by nitrogen plasma RPECVD is increased fourfold. Growths of buffered GaN show an XRD intensity increase by four times with smaller FWHM, half the droplet roughness on the surface as identical recipe unbuffered GaN growths, and are believed to show superior electrical properties. An increase to lateral growth, crystallite nucleation and nitrided metal coalescence from the buffer layer are believed to account for the improvements. The same buffer layers also improve the quality of p-type GaN fourfold, when grown by similar recipes to the GaN. A low carrier concentration is identified by Hall effect, which seems to indicate that the solubility limit of magnesium in gallium droplets is being reached; since at this limit and room temperature the hole concentration after this doping should be of the magnitude of the background electron concentration of GaN grown by the system. AFM smoothness figures also show improvement, with optical transmission characteristics indicating an empty conduction band edge. Finally, calculation is performed using the linear combination of atomic orbitals method (LCAO) of the electron band structure of intermittent stoichiometry values between various types of primitive cells occurring in InGaN growths contaminated with background oxygen. The intermittent stoichiometry bandstructure between InN and GaN is important because it represents the bandstructure of the gradient of diffusion of indium into GaN at phase separation boundaries 7 between isolated phases of InN and GaN in InGaN growths. Calculations of oxygen on intermittent InN stoichiometries identifies it as a viable culprit for the yellow electroluminescence defect seen in InGaN light emitting devices. Calculations of the real part of dielectric susceptibility are performed on InGaN contaminated with oxygen; as well as in indium rich conditions of InGaN with indium substituted for nitrogen in the cell