M.C. Luo

Epitaxial growth and characterization of SiC on C-plane sapphire substrates by ammonia nitridation

The growth of SiC epilayers on C-face (0 0 0 1) sapphire (alpha-Al2O3) has been performed using CVD method. We found that the quality of SiC epilayers has been improved through the nitridation of substrates by exposing them to ammonia ambient, as compared to growth on bare sapphire substrates. The single crystallinity of these layers was verified by XRD and double crystal XRD measurements. Atomic force microscopy was used to evaluate the surface morphology. Infrared reflectivity and Raman scattering measurement were carried out to investigate the phonon modes in the grown SiC. Detailed Raman analysis identified the 6H nature of the as-grown SiC films

Structural properties and Raman measurement of AlN films grown on Si (111) by NH3-GSMBE

Epitaxial growth of AlN has been performed by molecular beam epitaxy (MBE) with ammonia. The structural properties of materials were studied by cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). XRD and TEM diffraction pattern confirm the AlN is single crystalline 2H-polytype with the epitaxial relationship of (0001)AlNparallel to(111)Si, [11 (2) over bar0](AlN)parallel to[110](Si), [10 (1) over bar0](AlN)parallel to[11 (2) over bar](Si). Micro-Raman scattering measurement shows that the E-2 (high) and A(1) (LO) phonon mode shift 9 cm(-1) toward the low frequency, which shows the existence of large tensile strain in the AlN films. Furthermore, the appearance of forbidden A, (TO) mode and its anomalous shift toward high frequency was found and explained

Visible blind p+-π-n--n+ ultraviolet photodetectors based on 4H-SiC homoepilayers

p^+-@p-n^--n^+ ultraviolet photodetectors based on 4H-SiC homoepilayers have been presented. The growth of the 4H-SiC homoepilayers was carried out in a LPCVD system. The size of the active area of the photodetectors was 300x300@mm^2. The dark and illuminated I-V characteristics had been measured at reverse biases form 0 to 20V at room temperature, and the illuminated current was at least two orders of magnitude than that of dark current below 13V bias. The peak value zones of the photoresponse were located at 280-310nm at different reverse biases, and the peak value located at 300nm was 100 times greater than the cut-off response value in 380nm at a bias of 10V, which showed the device had good visible blind performance. A small red-shift about 5nm on the peak responsivity occurred when reverse bias increased from 5 to 15V.

Micro-Raman Investigation of Defects in a 4H-SiC Homoepilayer

Three types of defects, namely defect I, defect II, defect III, in the 4H-SiC homoepilayer were investigated by micro-raman scattering measurement. These defects all originate from a certain core and are composed of (I) a wavy tail region, (II) two long tails, the so called comet and (III) three plaits. It was found that there are 3C-SiC inclusions in the cores of defect II and defect III and the shape of inclusion determines the type of defect II or defect III. If the core contains a triangle-shaped inclusion, the defect III would be formed; otherwise, the defect II was formed. No inclusion was observed in the core of the defect I. The mechanisms of these defects are discussed.

Epitaxial growth of SiC on complex substrates

Epitaxial growth of SiC on complex substrates was carried out at substrate temperature from 1200 degreesC to 1400 degreesC. Three kinds of new complex substrates, c-plane sapphire, AlN/sapphire, and GaN/AlN/sapphire, were used in this study. We obtained a growth rate in the range of 1-6 mum/h. Thick (6 mum) SIC epitaxial layers with no cracks were successfully obtained on AlN/sapphire and GaN/AlN/sapphire substrates. X-ray diffraction patterns have confirmed that single-crystal SiC was obtained on these complex substrates. Analysis of optical transmission spectra of the SIC grown on sapphire substrates shows the lowest-energy gap near 2.2 eV, which is the value for cubic SiC. The undoped SIC showed n-type electrical conductivity

Preferential orientation growth of AIN thin films on Si (111) substrates by LP-MOCVD

Aluminum nitride (AlN) thin films were deposited on Si (111) substrates by low pressure metalorganic chemical vapor deposition system. The effects of the V/III ratios on the film structure and surface morphology were systematically studied. The chemical states and vibration modes of AlN films were characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. The optical absorption property of the AlN films, characterized by ultraviolet-visible-near infrared spectrophotometer, exhibited a sharp absorption near the wavelength of 206 nm. The AlN (002) preferential orientation growth was obtained at the V/III ratio of 10,000 and the preferential growth mechanism is presented in this paper according to the thermodynamics and kinetics process of the AlN growth.

Homoepitaxial growth of 4H-SiC multi-epilayers and its application to UV detection

Homoepitaxial growth of 4H-SiC p+/π/n- multi-epilayer on n+ substrate and in-situ doping of p+ and π-epilayer have been achieved in the LPCVD system with SiH4+C2H4+H2. The surface morphologies, homogeneities and doping concentrations of the n--single-epilayers and the p+/π/n- multi-epilayers were investigated by Nomarski, AFM, Raman and SIMS, respectively. AFM and Raman investigation showed that both single- and multi-epilayers have good surface morphologies and homogeneities, and the SIMS analyses indicated the boron concentration in p+ layer was at least 100 times higher than that in π layer. The UV photodetectors fabricated on 4H-SiC p+/π/n- multi-epilayers showed low dark current and high detectivity in the UV range.

Visible blind p+/p/n-/n+ UV 4H-SiC photodiodes based on 4H-SiC homoepilayers

The p⁺/p^-/n^-/n⁺ structure ultraviolet 4H-SiC photodiodes with different sizes of active areas have been fabricated and characterized by the I-V characteristics and photoresponse spectra. The statistical leakage current was around 10 ^-11nA at zero bias and it was less than 10^-9 A at -5 V obtained from the 100 times 100 mum² size samples. The photoresponse spectra, measured at different biases, showed high detectivity at ultraviolet range of 330-360nm, which means that the photodiodes have excellent performance in the detection of the solar ultraviolet light

Effects of V/III Ratios on the Properties of AlN Grown on Si (111) Substrate by LP-MOCVD

The AlN thin films were deposited on Si(111) substrates by home-made low pressure metalorganic chemical vapor deposition (LP-MOCVD). At the growth temperature of 1100degC, the effects of the different V/III ratios on the surface morphology and structural characteristics of AlN films were systematically studied. The growth rate of about 150 nm/h was determined by the cross-sectional SEM. By the help of X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements, the obvious effects of the specific growth conditions (different V/III ratios) on the surface morphology and crystallinity of the deposited AlN films were investigated. At the V/III ratio of 15000, the preferred (0002) orientated AlN epitaxial film with the relatively smaller RMS roughness (1.422 nm) was obtained. X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical composition and the chemical bonding structure of the AlN film, indicating some Si atoms outdiffusion from the Si substrate occurred

Homoepitaxial Growth and Device Characteristics of SiC on Off-Oriented Si-Face (0001) 4H-SiC

Homoepitaxial growth of unintentional doped, nitrogen (N) doped n-type, and boron (B) doped p-type 4H-SiC epilayers on off-oriented n-type and semi-insulating Si-face (0001) substrates was performed in a horizontal hot-wall chemical vapor deposition (HW-CVD) reactor with SiH 4 and C2H4 at temperature of 1500 degC and pressure of 40 Torr. The electrical and structural properties, and intentional in-situ doping in 4H-SiC epilayers were investigated by using room temperature Hall effect measurement, Raman scattering measurement, and secondary ion mass spectroscopy (SIMS). PiN and MESFET structural materials were obtained by growing B-doped and undoped 4H-SiC epitaxial layers on n-type substrates and N-doped and undoped on semi-insulating substrates, respectively. The I-V characteristics of high power PiN rectifiers, UV PiN detectors and MESFETs were presented