N-polar GaN film was obtained by using a high-temperature AlN buffer layer.It was found that the polarity could be inverted by a thin low-temperature AlN interlayer with the same V/III ratio as that of the high-temper...N-polar GaN film was obtained by using a high-temperature AlN buffer layer.It was found that the polarity could be inverted by a thin low-temperature AlN interlayer with the same V/III ratio as that of the high-temperature AlN layer.Continuing to increase the V/III ratio of the low-temperature AlN interlayer,the Ga-polarity of GaN film was inverted to N-polarity again but the crystal quality and surface roughness of GaN film greatly deteriorated.Finally,we analyzed the chemical environment of the AlN layer by x-ray photoelectron spectroscopy(XPS),which provides a new direction for the control of GaN polarity.展开更多
Gallium nitride(GaN) thin film of the nitrogen polarity(N-polar) was grown on C-plane sapphire and misoriented C-plane sapphire substrates respectively by metal-organic chemical vapor deposition(MOCVD). The misorienta...Gallium nitride(GaN) thin film of the nitrogen polarity(N-polar) was grown on C-plane sapphire and misoriented C-plane sapphire substrates respectively by metal-organic chemical vapor deposition(MOCVD). The misorientation angle is off-axis from C-plane toward M-plane of the substrates, and the angle is 2°and 4°respectively. The nitrogen polarity was confirmed by examining the images of the scanning electron microscope before and after the wet etching in potassium hydroxide(KOH) solution. The morphology was studied by the optical microscope and atomic force microscope. The crystalline quality was characterized by the x-ray diffraction. The lateral coherence length, the tilt angle, the vertical coherence length, and the vertical lattice-strain were acquired using the pseudo-Voigt function to fit the x-ray diffraction curves and then calculating with four empirical formulae. The lateral coherence length increases with the misorientation angle, because higher step density and shorter distance between adjacent steps can lead to larger lateral coherence length.The tilt angle increases with the misorientation angle, which means that the misoriented substrate can degrade the identity of crystal orientation of the N-polar GaN film. The vertical lattice-strain decreases with the misorientation angle. The vertical coherence length does not change a lot as the misorientation angle increases and this value of all samples is close to the nominal thickness of the N-polar GaN layer. This study helps to understand the influence of the misorientation angle of misoriented C-plane sapphire on the morphology, the crystalline quality, and the microstructure of N-polar GaN films.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.62004218)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB33000000).
文摘N-polar GaN film was obtained by using a high-temperature AlN buffer layer.It was found that the polarity could be inverted by a thin low-temperature AlN interlayer with the same V/III ratio as that of the high-temperature AlN layer.Continuing to increase the V/III ratio of the low-temperature AlN interlayer,the Ga-polarity of GaN film was inverted to N-polarity again but the crystal quality and surface roughness of GaN film greatly deteriorated.Finally,we analyzed the chemical environment of the AlN layer by x-ray photoelectron spectroscopy(XPS),which provides a new direction for the control of GaN polarity.
基金supported by the National Natural Science Foundation of China (Grant No. 61991441)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB33000000)Youth Innovation Promotion Association of Chinese Academy of Sciences。
文摘Gallium nitride(GaN) thin film of the nitrogen polarity(N-polar) was grown on C-plane sapphire and misoriented C-plane sapphire substrates respectively by metal-organic chemical vapor deposition(MOCVD). The misorientation angle is off-axis from C-plane toward M-plane of the substrates, and the angle is 2°and 4°respectively. The nitrogen polarity was confirmed by examining the images of the scanning electron microscope before and after the wet etching in potassium hydroxide(KOH) solution. The morphology was studied by the optical microscope and atomic force microscope. The crystalline quality was characterized by the x-ray diffraction. The lateral coherence length, the tilt angle, the vertical coherence length, and the vertical lattice-strain were acquired using the pseudo-Voigt function to fit the x-ray diffraction curves and then calculating with four empirical formulae. The lateral coherence length increases with the misorientation angle, because higher step density and shorter distance between adjacent steps can lead to larger lateral coherence length.The tilt angle increases with the misorientation angle, which means that the misoriented substrate can degrade the identity of crystal orientation of the N-polar GaN film. The vertical lattice-strain decreases with the misorientation angle. The vertical coherence length does not change a lot as the misorientation angle increases and this value of all samples is close to the nominal thickness of the N-polar GaN layer. This study helps to understand the influence of the misorientation angle of misoriented C-plane sapphire on the morphology, the crystalline quality, and the microstructure of N-polar GaN films.
