Preparation And Characterization Of The Al_1-xIn_xN Films

In recent years, III-V semiconductor materials have many potential applications in short-wavelength optoelectronic devices, including light emitting diodes (LEDs), laser diodes (LDs), ultraviolet detectors and high frequency and high power devices because of their advantage in wide direct band gap, high thermal conductivity and good chemical stability, etc. In above applications, the short-wavelength LED has great market potential in high density optical information storage, solid-state lighting and communication. ThereforeⅢ-Ⅴsemiconductor materials have been the focus of research these years. And in these materials, Al1-xInxN, as a new kind of ternary alloy, has attracted vast attention.Due to the different band gap between AIN (Eg=6.2eV) and InN (Eg=0.7eV), the band gap of Al1-xInxN could change with different parameter x, and it is an excellent luminescent material whose wavelength covers from ultraviolet to near-infrared wavelength regions. The lattice constant of Al0.83In0.17N is predicted to be the same as that of GaN. The Al0.83In0.17N/GaN heterojunctions have been proposed as active layers for field-effect transisitors (FETs) or Braggs mirrors because they are predicted to have few interface defects and high carrier density. But due to the huge difference in bond length and thermal stability between AIN and InN, the preparation of high crystalline quality Al1-xInxN is always a problem in researchers. There were few reports about high crystalline quality Al1-xInxN yet. In this paper, the AIN and Al1-xInxN films were prepared on sapphire substrates with MOCVD method, and the structural and optical properties of films were researched.The major work and results are as follows:1. AIN films were fabricated on sapphire (0001) with MOCVD method. High purity trimethyl aluminum A1(CH3)3 (TMA) was employed as Al organometallic (OM) source, NH3 as nitridizing agent and N2 as carrier gas. The growth temperature was varied from 700 to 1100℃, and the pressure in chamber from 1.5 to 50 Torr. The N/Al supply ratio was changed from 200/1 to 4000/1. The structural properties of samples were investigated in detail by x-ray diffraction. The films prepared at 900℃had better crystalline quality than others. The films grew slowly at low temperature, and strong vapor-phase reaction between TMA and NH3 was easier taken at high temperature which was detrimental to crystal growth. High pressure in chamber would make the vapor-phase reaction strong. The surface migration of Al atoms could be enhanced in low pressure, which reduced the surface roughness. DifferentⅢ-Ⅴsupply ratio could also influence the crystalline quality.2. Al1-xInxN films were fabricated on sapphire (0001) with MOCVD method. High purity trimethyl aluminum A1(CH3)3 (TMA) was employed as Al organometallic (OM) source, trimethyl indium In(CH3)3 (TMIn) as In OM source, NH3 as nitridizing agent and N2 as carrier gas. The growth temperature was varied from 700 to 900℃, and the pressure in chamber was kept at 1.5 Torr. The composition x was varied from 0.1 to 0.6. The structural properties of samples were investigated in detail by x-ray diffraction. All the films were polycrystalline with wurtzite structure. The lattice constant was increased with composition x, but band gap was decreased. The composition of films was investigated in detail by X-ray Photoelectron Spectroscopy. The In content was decreased with growth temperature increasing, which may be attribute to the desorption of In atom at high temperature. The In content of samples was not linear with TMIn supply flow, which may be ascribed to the mismatch between films and substrates. The growth rate of films was decreased with composition x increasing.