Improved crystal quality of GaN film with the in-plane lattice-matched Ino.17Alo.s3N interlayer grown on sapphire substrate using pulsed metal-organic chemical vapor deposition

We report on an improvement in the crystal quality of GaN film with an Ino.17Alo.83N interlayer grown by pulsed metal-organic chemical vapor deposition, which is in-plane lattice-matched to GaN films. The indium composition of about 17% and the reductions of both screw and edge threading dislocations （TDs） in GaN film with the InA1N interlayer are estimated by high resolution X-ray diffraction. Transmission electron microscopy （TEM） measurements are employed to understand the mechanism of reduction in TD density. Raman and photoluminescence measurements indicate that the InA1N interlayer can improve the crystal quality of GaN film, and verify that there is no additional residual stress induced into the GaN film with InA1N interlayer. Atomic force microscopy measurement shows that the InA1N interlayer brings in a smooth surface morphology of GaN film. All the results show that the insertion of the InA1N interlayer is a convenient method to achieve excellent crystal quality in GaN epitaxy.     

Semipolar(1122) and polar(0001) InGaN grown on sapphire substrate by using pulsed metal organic chemical vapor deposition

High indium semipolar(1122) and polar(0001) In Ga N layers each with a thickness of about 100 nm are realized simultaneously on sapphire substrates by pulsed metal organic chemical vapor deposition(MOCVD). The morphology evolution, structural and optical characteristics are also studied. The indium content in the layer of the surface(1122)is larger than that of the surface(0001), which is confirmed by reciprocal space map, photoluminescence spectrum and secondary ion mass spectrometer. Additionally, the(0001) surface with island-like morphology shows inhomogeneous indium incorporation, while the(1122) surface with a spiral-like morphology shows a better homogeneous In composition.This feature is also demonstrated by the monochromatic cathodoluminescence map.     

The influence of SixNy interlayer on GaN film grown on Si(111) substrate

A method to drastically reduce dislocation density in a GaN film grown on an Si(111) substrate is newly developed. In this method, the Si_xN_y interlayer which is deposited on an AlN buffer layer in situ is introduced to grow the GaN film laterally. The crack-free GaN film with thickness over 1.7 micron is grown on an Si(111) substrate successfully. Synthesized GaN epilayer is characterized by X-ray diffraction (XRD), atomic force microscope (AFM), and Raman spectrum. The test results show that the GaN crystal reveals a wurtzite structure with the <0001> crystal orientation and the full width at half maximum of the X-ray diffraction curve in the (0002) plane is as low as 403 arcsec for the GaN film grown on the Si substrate with an Si_xN_y interlayer. In addition, Raman scattering is used to study the stress in the sample. The results indicate that the Si_xN_y interlayer can more effectively accommodate the strain energy. So the dislocation density can be reduced drastically, and the crystal quality of GaN film can be greatly improved by introducing Si_xN_y interlayer.     

Influence of the channel electric field distribution on the polarization Coulomb field scattering in In0.18 Al0.82 N/AlN/GaN heterostructure field-effect transistors

By making use of the quasi-two-dimensional(quasi-2D) model, the current–voltage(I–V) characteristics of In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors(HFETs) with different gate lengths are simulated based on the measured capacitance–voltage(C–V) characteristics and I–V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas(2DEG) with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V·s for the prepared In0.18Al0.82N/AlN/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain–source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density,the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.