Study On The Electricial Properties Of P Type GaN-Bsaed Films

In recent years, as the third generation semiconductor materials, ?-nitride have been developed very rapidly, but there are still many problems. In particular, getting ideal electrical performance is always difficult for GaN-based materials.Mg-doped polar, semi-polar, nonpolar GaN and AlGaN epitaxial films were grown on the sapphire substrates with various polarity by MOCVD in this study. The surface morphology and crystal quality was characterized, and the conditions of growth and thermal anneal were optimized to improve the electrical properties.The main research contents and the results achieved in this study are as follows:(1) Mg uniformly doped and delta doped GaN epitaxial layers were prepared on c-plane sapphire substrates, respectively. It was found that the electrical performance of p-GaN epitaxial film was improved significantly by using delta doping which can prevent the underlying dislocations from extending upward. The delta doped p-GaN film was annealed at various temperatures. It was shown that p-GaN film with the best electrical performance was achieved at 770 ?, and the hole concentration, mobility and resistivity were 1.09 × 1018cm-3? 2.83 cm2/V·s and 1.89?· m, respectively.(2) p-AlGaN epitaxial films were grown on c-plane sapphire substrate. The effect of inserting different buffer layers on the surface morphology, crystal quality and electrical properties was investigated. The experimental results showed that when the insert layer was undoped GaN layer, both surface morphology and electrical performance of AlGaN epitaxial layer were significantly improved. It was shown that the insertion of proper buffer layers can greatly improve the crystal quality of p-AlGaN films, resulting in reduced density of compensation acceptor, and enhanced hole concentration for the p-type layers. The conditions for delta doping of p-AIGaN epitaxial layer has been optimized. By varying the thickness of the p-AlGaN film while maintaining the same delta doping time, p-AlGaN films with different electrical properties were grown. And the best result was achieved when the p-AlGaN thickness was 10nm. The annealing conditions like temperature, time, atmosphere, heating rate, and gas flow rate were also optimized. The p-AlGaN film with the best electrical properties was obtained when the annealing temperature was 750 ?, the annealing time was 8 min, the annealing atmosphere was oxygen, the heating rate was 50 ?/s, and the gas flow rate was 800 sccm. At that time point, the resistivity was as low as 1.2 ?·cm.(3) The growth and p-type doping of semi-polar and nonpolar GaN and AlGaN films were also preliminarily studied in the paper. p-AlGaN films with various Al compositions were grown on m-plane sapphire substrates by using AlN buffer layer grown with ammonia pulse-flow method(AP-AlN). The transmission spectrum curve showed that AlGaN film with higher Al composition had an improved internal crystal quality. It was because that there was smaller lattice mismatch between AlGaN film with higher Al composition and AP-AlN buffer layer, which was beneficial to epitaxial growth. And it was induced from the characterization results of SEM, and XRD rocking curve for the semi-polar AlGaN film with various Mg-doping concentrations of 0,125,175 and 200 sccm that the higher the doping concentration, the rougher the surface morphology, and the larger the FWHM of XRD rocking curve, the poorer the crystal quality. Un-doped and Mg-doped GaN films were grown on r-plane sapphire substrate as well. SEM measurement results showed that Mg-doping can make the surface morphology rough, and the XRD rocking curve showed that FWHM along the c direction basically remain unchanged, but it had an obvious increase along the m direction, implying poorer crystal quality of the films.