High-resolution X-ray diffraction has been employed to investigate the diffuse scattering in a （0001） oriented GaN epitaxial film grown on sapphire substrate. The analysis reveals that defect clusters are present in GaN films and their concentration increases as the density of threading dislocations increases. Meanwhile, the mean radius of these defect clus- ters shows a reverse tendency. This result is explained by the effect of clusters preferentially forming around dislocations, which act as effective sinks for the segregation of point defects. The electric mobility is found to decrease as the cluster concentration increases.
This paper reports that Al1-xInxN epilayers were grown on GaN template by metalorganic chemical vapor deposition with an In content of 7%--20%. X-ray diffraction results indicate that all these Al1-xInxN epilayers have a relatively low density of threading dislocations. Rutherford backscattering/channeling measurements provide the exact compositional information and show that a gradual variation in composition of the Al1-xInxN epilayer happens along the growth direction. The experimental results of optical reflection clearly show the bandgap energies of Al1-xInxN epilayers. A bowing parameter of 6.5~eV is obtained from the compositional dependence of the energy gap. The cathodoluminescence peak energy of the Al1-xInxN epilayer is much lower than its bandgap, indicating a relatively large Stokes shift in the Al1-xInxN sample.
A violet laser diode （LD） structure is grown on a free-standing c-plane GaN substrate and 4 μm×800μm ridge waveguide LDs are fabricated. The electrical and the optical characteristics of LDs under different facet-coating and chip-mounting conditions are investigated under pulse mode operation. The active region temperatures of p-side up and p-side down mounted LDs are calculated with different injection currents. The calculated thermal resistances of p-side up and p-side down mounted LDs are 4.6 K/W and 3 K/W, respectively. The threshold current of the p-side down mounted LD is much lower than that of the p-side up mounted LD. The blue shift of the emission wavelength with increasing injection current is observed only for the LD with p-side down mounting configuration, due to the more efficient heat dissipation.
Mg-doped GaN layers prepared by metalorganic chemical vapor deposition were annealed at temperatures between 550 and 950℃. Room temperature （RT） Hall and photoluminescence （PL） spectroscopy measurements were performed on the as-grown and annealed samples. After annealing at 850℃, a high hole concentration of 8 × 10^17 cm^-3 and a resistivity of 0. 8lΩ·cm are obtained. Two dominant defect-related PL emission bands in GaN.. Mg are investigated; the blue band is centered at 2. 8eV （BL） and the ultraviolet emission band is around 3.27eV （UVL）. The relative intensity of BL to UVL increases after annealing at 550℃, but decreases when the annealing temperature is raised from 650 to 850℃, and finally increases sharply when the annealing temperature is raised to 950~C. The hole concentration increases with increased Mg doping, and decreases for higher Mg doping concentrations. These results indicate that the difficulties in achieving high hole concentration of 10^18cm^-3 appear to be related not only to hydrogen passivation, but also to self-compensation.
To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au （5 nm/5 nm） film deposition. The surface morphology of wafers and the current voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.
High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single A1GaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si （111） substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlCaN interlayer on the structural properties of the resulting CaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AIGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated.
对采用MOCVD(metalorganic chemical vapor phase deposition)技术生长在GaN/Sapphire衬底上的InN薄膜进行了Hall、吸收谱以及低温光致发光(photoluminescence,PL)谱的测量和分析.Hall测量发现,样品的载流子浓度分布在1018～1019cm-3.在10K温度下进行PL测量,并对其线形进行分析,得到InN的带隙在0.7eV左右.综合Hall、吸收谱及PL谱的结果发现,吸收边以及PL谱的峰值能量都随载流子浓度的增加而蓝移.此外,我们还讨论了由吸收谱计算InN带隙的存在的不确定性.
We present the growth of CaN epilayer on Si （111） substrate with a single A1GaN interlayer sandwiched between the GaN epilayer and A1N buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an A1N buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.
