Study On Epitaxy Of Gan Hemt Structure On Si Substrate

Gallium Nitride semiconductor materials have the advantages of wide bandgap,high electron saturation velocity, high thermal conductivity and high breakdownvoltage. Moreover, AlGaN/GaN heterostructure possess strong spontaneous andpiezoelectric effect, creating high density (1013cm-2) of two-dimensional electron gas(2DEG) in the channel of heterostructure, even though the AlGaN barrier layer withoutdoping. In addition, since there are very few impurities in the GaN channel, so theimpurity scattering process almost not diminish the2DEG mobility, which can achieve2000cm2/Vs. AlGaN/GaN HEMT devices have great potential on high power, highfrequency and high voltage applications.In this paper, GaN materials were grown on Si substrates by metalorganic chemicalvapor deposition (MOCVD), and learn from the experience of depositionAlGaN/AlN/GaN heterostructure on sapphire substrates, exploring the method ofgrowth AlGaN/AlN/GaN HEMT structure materials on Si substrate. The major workare listed as below.1. The influence of AlN buffer layer thickness on GaN epitaxial film on Si substratewere investigated. It is observed that as the AlN buffer with thickness of15nm, the GaNlayer has no crack and the in-plane tension stress is0.3GPa, with the full width at halfmaximum as low as536arcsec for (0002) and594arcsec for the (10-12) reflection, therms roughness tested by atomic force microscopy is0.2nm, which is one of the goodresults for GaN on Si substrates in China.2. The method of growth GaN films on Si substrate using an AlGaN stress releaseinterlayer was explored. By introducing an Al0.23Ga0.77N stress release interlayerbetween the AlN buffer and the GaN epitaxial film, we obtained2μm GaN film whichhas no crack in the central region of the wafer.3. Influence of AlN interfacial layer on properties of AlGaN/AlN/GaN HEMT wereinvestigated. It is observed that the AlN interfacial layer can increase the conductionband discontinuity between AlGaN barrier layer and GaN channel layer and reduce thealloy disorder scattering process of AlGaN layer, significantly increase the2DEGdensity and mobility. The HEMT material with an AlN interfacial layer thickness of1.5nm showed a high2DEG density of1.2×1013cm-2with a sheet resistance of310/□,and Hall mobility of1680cm2/Vs were obtained at room temperature.4. Electrical properties of AlxGa1-xN/AlN/GaN HEMT materials with different Al compositions (x=0.19,0.22,0.25,0.32) were analyzed. It is observed that AlxGa1-xNbarrier layer with an Al composition of25%, the HEMT material showed a high2DEGdensity and mobility, with the lowest sheet resistance.5. Exploration of AlGaN/AlN/GaN HEMT material deposition on Si substrate, weobtained a HEMT on Si showed a2DEG density of7.98×1012cm-2with a sheetresistance of829/□, and Hall mobility of943cm2/Vs were obtained at roomtemperature.