The Applications Of Ⅲ-Nitrides Polarization Engineering In Optoelectronic And Tunneling Devices

Being non-centro symmetric and high degree ionicity, wurtzite Ill-nitrides exhibit strong spontaneous and piezoelectric polarization effects, which present the combining properties of polarization and semiconducting. The recent research reported by the groups from domestic and overseas demonstrated that polarization effect plays the role of a double-edged sword in III-nitrides, acting both negatively and positively. It is a meaningful subject to adopt the good points and avoid the shortcomings of polarization effect through the reasonable understanding and utilization of its properties. In this dissertation, based on the polarization phenomena and polarization theory, focus on the properties and characteristics of polarization field and polarization effect, we carried out the study of application of III-nitrides polarization engineering in emitter device and tunneling device, through the aspects of polarization regulation, polarization induction and polarization reverse. The main research and results are as follows:(1) The intensities, type, origin of stress of GaN epilayers grown on sapphire and6H-SiC substrate were investigated. GaN epilayers grown on sapphire was under compressive stress, while under tensile stress grown on6H-SiC substrate. Both of the stree intensities were at the level of GPa. Under similar stress intensities, dut to the differernce of buffer technique and stress type, the GaN film grown on sapphire had better crystalline quality and optical properties relative to the GaN epilayer on6H-SiC. The compressive stress of GaN grown on sapphire plusing with the compressive stress between InGaN well and GaN barrier contribute to the piezoelectric polarization field in MQWs. Therefore, the stress should be regluted to weaken the negative influence of QCSE on LED.(2) Based on the concept of polarization-regulated engineering, a500nm InGaN interlayer was grown before InGaN/GaN MQWs to fabricate red LED with emission wavelength of710nm. With the increase of driving current from20mA to100mA, the magnitude of blueshift of red LED is only13nm. The investigation indicates that thick-film InGaN interlayer can relax the compressive stress of GaN epilayer resulting from the sapphire substrate and regulate the strain field in MQWs. Moreover, the InGaN interlayer can decrease the turn-on voltage, improve the lumilenscense of chip and extend the emission wavelength of LED, which are beneficial for the development of long wavelength LED.(3) Based on the concept of polarization-induced engineering, using low Al-composition AlGaN as polarization-induced layer, Ⅲ-Ⅴ nitrides inter-band polarization-induced tunneling junctions (PITJs) were grown by MOCVD on planar sapphire substrate using conventional GaN epitaxial processing. The forward negative-differential-resistance (NDR) device presents forward NDR effect at3.67V (the peak current is22.4mA with peak-valley ratio at9). The backward diode presents reverse current of3A-cm-2at-1V. respectively. The physical mechanisms of PITJs were presented through calculations based on self-consistent solution of Poisson-Schrodinger equations combined with polarization-induced theory.(4) The reversed polarization yellow emission InGaN/GaN multiple quantum wells (MQWs) in p-side down (PDMQWs) and n-side down (NDMQWs) structures were compared. The properties of PDMQWs and NDMQWs in surface morphology, interface quality, optical characteristic, and impurities distribution were investigated systematically. The potentials and problems, as well as the possible problem-solving methods of p-side down light-emitting diodes (PDLEDs) in developing long wavelength emitter were also discussed.(5) Mg-doped,1-μm-thick, p-type GaN films were grown by metal-organic chemical vapor deposition using indium-assisted method. The evolution process of indium-adlayer model considering adsorption, desorption and the transformation of indium mono-adlayer was proposed. Indium-assisted growth method can improve surface smoothness and crystalline quality of p-GaN effectively without affecting its electrical properties.(6) Based on the concept of polarization-reversed engineering, green (510nm) and yellow (600nm) polarization-reversed LEDs were fabricated with the combined utilization of indium-assisted growth of p-GaN and PITJ. The interface quality of MQWs was improved with the utilization of indium-assisted method. The turn-on voltage was decreased and the ability of current spreading and injection of PDLED was improved with the utilization of PITJ. The blue-shift of electroluminescence peak was little at the high working voltage.