Dongjuan Xi

Metal–semiconductor–metal GaN ultraviolet photodetectors on Si(111)

GaN metal–semiconductor–metal photoconductive detectors have been fabricated on Si(111) substrates. The GaN epitaxial layers were grown on Si substrates by means of metalorganic chemical-vapor deposition. These detectors exhibited a sharp cutoff at the wavelength of 363 nm and a high responsivity at a wavelength from 360 to 250 nm. A maximum responsivity of 6.9 A/W was achieved at 357 nm with a 5 V bias. The relationship between the responsivity and the bias voltage was measured. The responsivity saturated when the bias voltage reached 5 V. The response time of 4.8 ms was determined by the measurements of photocurrent versus modulation frequency.

Ti/Al/Pt/Au and Al ohmic contacts on Si-substrated GaN

Al and Ti/Al/Pt/Au ohmic contacts on GaN epitaxial layers were studied. The epilayers were grown on Si (111) substrates by low-pressure metalorganic chemical vapor deposition. Al/GaN contacts achieved a minimum contact resistivity of 7.5×10−3 Ω cm2 after annealing in N2 ambient at 450 °C for 3 min. Further annealing degraded the contacts. Ti/Al/Pt/Au and GaN contacts achieved a minimum contact resistivity of 8.4×10−5 Ω cm2 after annealing in N2 at 650 °C for 20 s. The Ti/Al/Pt/Au contacts on GaN showed a better thermal stability than Al/GaN contacts. After annealing at 600 °C for 30 min. they were still ohmic contacts. The mechanisms for ohmic contact formation of Ti/Al/Pt/Au contacts were also analyzed.

Study on strain and piezoelectric polarization of AlN thin films grown on Si

The strain and piezoelectric polarization of AlN thin films grown on Si(111) substrates by metalorganic chemical-vapor deposition were investigated by using x-ray diffraction and Raman measurements. The stress and piezoelectric polarization of the AlN films were analyzed with E2 (high) phonon-mode frequency shifts in Raman spectra. The result indicates that the biaxial compressive stress is about 4.3GPa, and the piezoelectric polarization is about 1.91×10−2C∕m2. Phonons of Si–N bonds were also observed accompanying phonons of AlN crystal in Raman spectra, which indicate the interdiffusion of Si and N atoms during growth.

Aluminum and GaN contacts on Si(111) and sapphire

Al and GaN contacts on both Si(111) and sapphire substrates were studied in this letter. After annealing at 450, 520, 600, and 650 °C for 35 min under a N2 flowing ambient, the current–voltage characteristics of Al/GaN contacts on Si(111) substrates were different from those on sapphire ones. The interfacial properties were discussed using the Schottky emission model in which the current is proportional to the square of the applied voltage. The metallurgical reactions were analyzed using photoluminescence (PL) spectra and x-ray diffraction (XRD). After annealing, blueshifts in the PL spectra and new peaks in the XRD data indicated that the wide-band gap interfacial phase AlGaN was formed at the Al/GaN interface.

Microstructures of AlGaN/AlN/Si (111) Grown by Metalorganic Chemical Vapor Deposition

In this paper the X-ray photoelectron spectrum and the Auger electron spectrum were used to study the microstructures of AlGaN/AlN/Si (111) grown by metal organic chemical vapor deposition. The results indicated that a broad transition region, about 20 nm, was present at the interface of AlN/Si and it was composed of AlN and SiN x (0 < x < 4/3). In AIN film the existence of Si-Si bonds was found. In the interface of AlGaN/AlN, the main incorporation form of N 1s varied gradually from AlN to the compound of GaN and AlN The diffusion of Si atoms was so strong at the high growth temperatures that the signal of Si 2p could be found throughout the epilayer.

Nitrogen diffusion in the Si growth on GaN by low-pressure chemical vapor deposition

Si film has been grown on a wurtzite gallium nitride layer on sapphire by low-pressure chemical vapor deposition. Uniform nitrogen incorporation was found in the Si film at the concentration of 5%, indicating an incorporation-limited process through interstitial diffusion from GaN layer to Si layer. The nitrogen occupied the substitutional sites in the Si film, leading this Si layer to be n-type doping with the carrier concentration of 1.42 x 10 1 8 /cm 3 and the hall mobility of 158 cm 2 /(V s). This is consistent with other calculated and experimental results, which suggest that only 5% nitrogen can occupy the substitutional sites in the nitrogen-doped Si materials.

Structural study of chemical vapor deposition of Si on GaN

We have grown high quality Si epilayers on wurtzite gallium nitride substrate by low-pressure chemical vapor deposition. X-ray photoelectron spectra and Auger electron spectra were employed to analyze the components and chemical structures of Si/GaN. The results indicated that there was nitrogen diffusion from the GaN layer to the Si layer and substitutional N accumulation near the interface, which agreed with carrier concentration obtained from electrical conductivity measurements.

Chemical structures of AlGaN/AlN/Si [111] by MOCVD using AES and XPS

In this paper X-ray photoelectron spectrum and Auger electron spectrum were used to study the microstructure of AlGaN/AlN/Si [111] grown by metal organic chemical vapor deposition. The results indicated that a broad transition region, composed of AlN, Si/sub 3/N/sub 4/, SiN/sub x/ (x<4/3) and Si was present at the interface of AlN/Si. At the interface of AlGaN/AlN, the main incorporation of N shifted from AlN to the compound of GaN and AlN gradually. The diffusion of Si atoms was very strong at the high growth temperatures and the signal of Si could be found in whole epilayers.

AlGaN/GaN/AlGaN ultraviolet photodetectors on Si

AlGaN/GaN/AlGaN ultraviolet photodetectors were grown on Si [111] substrates using an AlN buffer by metalorganic chemical vapor deposition. These detectors showed a high response in a narrow range of wavelength with a peak position at 365 nm. A peak responsivity of 24 A/W was obtained at 5.5 V bias. This high responsivity is mainly due to the high polarization electric-field in GaN layer of AlGaN/GaN/AlGaN heterojunction structure and the potential wells at AlGaN/GaN interfaces.