AIGaN/GaN high electron mobility transistors grown on sapphire substrates with a 0.3μm gate length and 100μm gate width are fabricated. The device reveals a drain current saturation density of 0.85A/mm at a gate voltage of 0V and a peak transconductance of 225mS/mm. The unity current gain cutoff frequency and maximum frequency of oscillation are obtained as 45 and 100GHz,respectively. The output power density and gain are 1.8W/mm and 9.5dB at 4GHz,and 1.12W/mm and 11.5dB at 8GHz.
AlGaN/AlN/GaN high electron mobility transistor （HEMT） structures with a high-mobility GaN thin layer as a channel are grown on high resistive 6H-SiC substrates by metalorganic chemical vapor deposition. The HEMT structure exhibits a typical two-dimensional electron gas （2DEG） mobility of 1944cm^2/（V·s） at room temperature and 11588cm^2/（V ·s） at 80K with almost equal 2DEG concentrations of about 1.03 × 10^13 cm^-2. High crystal quality of the HEMT structures is confirmed by triple-crystal X-ray diffraction analysis. Atomic force microscopy measurements reveal a smooth AlGaN surface with a root-mean-square roughness of 0.27nm for a scan area of 10μm × 10μm. HEMT devices with 0.8μm gate length and 1.2mm gate width are fabricated using the structures. A maximum drain current density of 957mA/mm and an extrinsic transconductance of 267mS/mm are obtained.
The surface morphology of GaN grown by MOCVD on GaN/Si template was studied.Rough morphology and deep pinhole defects on some surface areas of the samples were observed and studied.The formation of rough morphology is possibly related to Ga-Si alloy produced due to poor thermal stability of template at high temperature.The deep pinhole defects generated are deep down to the surface of MBE-grown GaN/Si template.The stress originated from the large thermal expansion coefficient difference between GaN and Si may be related to the formation of the pinhole defects.The surface morphology of the GaN can be improved by optimizing the GaN/Si template and decreasing the growth temperature.
Liu ZheWang JunxiWang XiaoliangHu GuoxinGuo LunchunLiu HongxinLi JianpingLi JinminZeng Yiping
High resistivity unintentionally doped GaN films were grown on (0001) sapphire substrates by metalorganic chemical vapor deposition. The surface morphology of the layer was measured by both atomic force microscopy and scanning electron microscopy. The results show that the films have mirror-like surface morphology with root mean square of 0.3 nm. The full width at half maximum of double crystal X-ray diffraction rocking curve for (0002) GaN is about 5.22 arcmin, indicative of high crystal quality. The resistivity of the GaN epilayers at room temperature and at 250 ℃ was measured to be approximate 109 and 106 Ω·cm respectively, by variable temperature Hall measurement. Deep level traps in the GaN epilayers were investigated by thermally stimulated current and resistivity measurements.
Fang Cebao Wang Xiaoliang Hu Guoxin Wang Junxi Wang Cuimei Li Jinmin
A theoretical calculation of the miscibility gap with considering the mismatch strain and elastic parameters was performed for the GaN1-xPx ternary alloys on (0001) GaN/sapphire substrates based on the strictly regular solution model. The calculated results show that the boundary of the spinodal isotherm shifts from x=0.06 to x=0.25 at the growth temperature of 1200 K as the strain factor increases from 0 to 1, indicating that the strain in the GaN1-xPx layers can suppress the phase separation. Meanwhile, with the increase of the effective elastic parameters of GaN and GaP, the available maximum P content also increases slightly at the growing temperature.
Zhang Kaixiao Chen Dunjun Zhu Weihua Lin Jianwei Zhang Rong Zheng Youdou
