This paper reports that the yellow luminescence intensity of N-polar GaN Epi-layers is much lower than that of Ga-polar ones due to the inverse polarity, and reduces drastically in the N-polar unintentionally-doped Ga...This paper reports that the yellow luminescence intensity of N-polar GaN Epi-layers is much lower than that of Ga-polar ones due to the inverse polarity, and reduces drastically in the N-polar unintentionally-doped GaN after etching in KOH solution. The ratio of yellow luminescence intensity to band-edge emission intensity decreases sharply with the etching time. The full width at half maximum of x-ray diffraction of （10-12） plane falls sharply after etching, and the surface morphology characterized by scanning electron microscope shows a rough surface that changes with the etching time. The mechanism for the generation of the yellow luminescence are explained in details.展开更多
Ti/Al based Ohmic contacts to as-grown N-polar GaN are investigated by cross-section transmission electron microscopy and energy dispersive x-ray spectroscopy. Due to the higher oxygen background doping in the N- pola...Ti/Al based Ohmic contacts to as-grown N-polar GaN are investigated by cross-section transmission electron microscopy and energy dispersive x-ray spectroscopy. Due to the higher oxygen background doping in the N- polar GaN, the A1 metal in Ohmic stacks is found to react with background oxygen more easily, resulting in more AlOe. In addition, the formation of AlOx is affected by the A1 layer thickness greatly. The AlOx combined with the presence of AIN is detrimental to the Ohmic contacts for N-polar GaN compared with Ga-polar GaN. With the reduction of the AI layer thickness to some extent, less AlOx and AIN are formed, and lower Ohmic contact resistance is obtained. The lowest contact resistivity p of 1.97 × 10-6 Ω·cm2 is achieved with the AI layer thickness of 80 nm.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
The growth and properties of N-polar Ga N layers by metal organic chemical vapor deposition（MOCVD） were reported. It is found that N-polar Ga N grown on normal sapphire substrate shows hexagonal hillock surface morp...The growth and properties of N-polar Ga N layers by metal organic chemical vapor deposition（MOCVD） were reported. It is found that N-polar Ga N grown on normal sapphire substrate shows hexagonal hillock surface morphology. With the misorientation angles increasing from 0.5° to 2.0° toward the a-plane of the sapphire substrate, the number of the hillock becomes less and less and finally the surface becomes flat one on the sapphire substrate with the misorientation angle of 2°. It is also found that the crystalline quality and the strain in the Ga N are greatly influenced by the misorientation angle.展开更多
We reported the growth of N-polar InN films on N-polar GaN/sapphire substrates by pulsed metal-organic vapor phase epitaxy. The crystalline quality, surface morphology, optical and electrical properties of N-polar InN...We reported the growth of N-polar InN films on N-polar GaN/sapphire substrates by pulsed metal-organic vapor phase epitaxy. The crystalline quality, surface morphology, optical and electrical properties of N-polar InN films were investigated in details by varying the breaking time and trimethylindium（TMIn） duration of pulse cycle. It has been found that when the breaking time and the TMIn duration in each cycle remain at 30 and 60 s, respectively, the N-polar InN film obtained exhibits a better crystalline quality and greater optical properties. Meanwhile, the surface morphology and electrical properties of the N-polar InN films also greatly depend on the given growth conditions.展开更多
基金supported by the National Key Science & Technology Special Project (Grant No. 2008ZX01002-002)the Major Programand Key Program of National Natural Science Foundation of China (Grant Nos. 60890191 and 60736033)the Chinese Advance Research Program of Science and Technology (Grant Nos. 51308040301,51308030102,51311050112,and 51323030207)
文摘This paper reports that the yellow luminescence intensity of N-polar GaN Epi-layers is much lower than that of Ga-polar ones due to the inverse polarity, and reduces drastically in the N-polar unintentionally-doped GaN after etching in KOH solution. The ratio of yellow luminescence intensity to band-edge emission intensity decreases sharply with the etching time. The full width at half maximum of x-ray diffraction of （10-12） plane falls sharply after etching, and the surface morphology characterized by scanning electron microscope shows a rough surface that changes with the etching time. The mechanism for the generation of the yellow luminescence are explained in details.
基金Supported by the National Natural Science Foundation of China under Grant No 61306113
文摘Ti/Al based Ohmic contacts to as-grown N-polar GaN are investigated by cross-section transmission electron microscopy and energy dispersive x-ray spectroscopy. Due to the higher oxygen background doping in the N- polar GaN, the A1 metal in Ohmic stacks is found to react with background oxygen more easily, resulting in more AlOe. In addition, the formation of AlOx is affected by the A1 layer thickness greatly. The AlOx combined with the presence of AIN is detrimental to the Ohmic contacts for N-polar GaN compared with Ga-polar GaN. With the reduction of the AI layer thickness to some extent, less AlOx and AIN are formed, and lower Ohmic contact resistance is obtained. The lowest contact resistivity p of 1.97 × 10-6 Ω·cm2 is achieved with the AI layer thickness of 80 nm.
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.
基金Project supported by the National Natural Science Foundation of China （Grant No 60606021）, the Specialized Research Fund for the Doctoral Program of Higher Education of China （Grant No 20060003067） and the Key Fundamental Research Foundation of Tsinghua University of China （Grant No Jz2001010）.
基金financially supported by the National Basic Research Program of China (Nos. 2012CB619303 and 2012CB619304)the National Natural Science Foundation of China (Nos. 11023003, 10990102, 11174008 and 61076012)the National High Technology Research & Development Project of China (No. 2011AA03A103)
文摘The growth and properties of N-polar Ga N layers by metal organic chemical vapor deposition（MOCVD） were reported. It is found that N-polar Ga N grown on normal sapphire substrate shows hexagonal hillock surface morphology. With the misorientation angles increasing from 0.5° to 2.0° toward the a-plane of the sapphire substrate, the number of the hillock becomes less and less and finally the surface becomes flat one on the sapphire substrate with the misorientation angle of 2°. It is also found that the crystalline quality and the strain in the Ga N are greatly influenced by the misorientation angle.
文摘We reported the growth of N-polar InN films on N-polar GaN/sapphire substrates by pulsed metal-organic vapor phase epitaxy. The crystalline quality, surface morphology, optical and electrical properties of N-polar InN films were investigated in details by varying the breaking time and trimethylindium（TMIn） duration of pulse cycle. It has been found that when the breaking time and the TMIn duration in each cycle remain at 30 and 60 s, respectively, the N-polar InN film obtained exhibits a better crystalline quality and greater optical properties. Meanwhile, the surface morphology and electrical properties of the N-polar InN films also greatly depend on the given growth conditions.
