In-Situ Boron and Aluminum Doping and Their Memory Effects in 4H-SiC Homoepitaxial Layers Grown by Hot-Wall LPCVD

The in-situ p-type doping of 4H-SiC grown on off-oriented (0001) 4H-SiC substrates was performed with trimethylaluminum (TMA) and/or diborane (B2H6) as the dopants. The incorporations of Al and B atoms and their memory effects and the electrical properties of p-type 4H-SiC epilayers were characterized by secondary ion mass spectroscopy (SIMS) and Hall effect measurements, respectively. Both Al- and B-doped 4H-SiC epilayers were p-type conduction. It was shown that the profiles of the incorporated boron and aluminum concentration were in agreement with the designed TMA and B2H6 flow rate diagrams. The maximum hole concentration for the Al doped 4H-SiC was 3.52x10(20) cm(-3) with Hall mobility of about 1 cm(2)/Vs and resistivity of 1.6 similar to 2.2x10(-2) Omega cm. The heavily boron-doped 4H-SiC samples were also obtained with B2H6 gas flow rate of 5 sccm, yielding values of 0.328 Omega cm for resistivity, 5.3x10(18) cm(-3) for hole carrier concentration, and 7 cm(2)/VS for hole mobility. The doping efficiency of Al in SiC is larger than that of B. The memory effects of Al and B were investigated in undoped 4H-SiC by using SIMS measurement after a few run of doped 4H-SiC growth. It was clearly shown that the memory effect of Al is stronger than that of B. It is suggested that p-type 4H-SiC growth should be carried out in a separate reactor, especially for Al doping, in order to avoid the join contamination on the subsequent n-type growth. 4H-SiC PiN diodes were fabricated by using heavily B doped epilayers. Preliminary results of PiN diodes with blocking voltage of 300 V and forward voltage drop of 3.0 V were obtained.

Heteroepitaxial Growth of 3C-SiC on Si (111) Substrate using AlN as a Buffer Layer

Using AlN as a buffer layer, 3C-SiC film has been grown on Si substrate by low pressure chemical vapor deposition (LPCVD). Firstly growth of AlN thin films on Si substrates under varied V/III ratios at 1100 degrees was investigated and the (002) preferred orientational growth with good crystallinity was obtained at the V/III ratio of 10000. Annealing at 1300 degrees C indicated the surface morphology and crystallinity stability of AlN film. Secondly the 3C-SiC film was grown on Si substrate with AlN buffer layer. Compared to that without AlN buffer layer, the crystal quality of the 3C-SiC film was improved on the AlN/Si substrate, characterized by X-ray diffraction (XRD) and Raman measurements.

Homoepitaxial growth and characterization of 4H-SiC epilayers by low-pressure hot-wall chemical vapor deposition

Horizontal air-cooled low-pressure hot-wall CVD (LP-HWCVD) system is developed to get high quality 4H-SiC epilayers. Homoepitaxial growth of 4H-SiC on off-oriented Si-face (0001) 4H-SiC substrates purchased from Cree is performed at a typical temperature of 1500 degrees C with a pressure of 40 Torr by using SiH4+C2H4+H-2 gas system. The surface morphologies and structural and optical properties of 4H-SiC epilayers are characterized with Nomarski optical microscope, atomic force microscopy (AFM), x-ray diffraction, Raman scattering, and low temperature photoluminescence (LTPL). The background doping of 32 pm-thick sample has been reduced to 2-5 x 10(15) cm(-3). The FWHM of the rocking curve is 9-16 arcsec. Intentional N-doped and B-doped 4H-SiC epilayers are obtained by in-situ doping of NH3 and B2H6, respectively. Schottky barrier diodes with reverse blocking voltage of over 1000 V are achieved preliminarily.

Self-assembled GaAs quantum rings by MBE droplet epitaxy

Fabrication of semiconductor nanostructures such as quantum dots (QDs), quantum rings (QRs) has been considered as the important step for realization of solid state quantum information devices, including QDs single photon emission source, QRs single electron memory unit, etc. To fabricate GaAs quantum rings, we use Molecular Beam Epitaxy (MBE) droplet technique in this report. In this droplet technique, Gallium (Ga) molecular beams are supplied initially without Arsenic (As) ambience, forming droplet-like nano-clusters of Ga atoms on the substrate, then the Arsenic beams are supplied to crystallize the Ga droplets into GaAs crystals. Because the morphologies and dimensions of the GaAs crystal are governed by the interplay between the surface migration of Ga and As adatoms and their crystallization, the shape of the GaAs crystals can be modified into rings, and the size and density can be controlled by varying the growth temperatures and As/Ga flux beam equivalent pressures(BEPs). It has been shown by Atomic force microscope (AFM) measurements that GaAs single rings, concentric double rings and coupled double rings are grown successfully at typical growth temperatures of 200 C to 300 C under As flux (BEP) of about 1.0 x 10(-6) Torr. The diameter of GaAs rings is about 30-50 nm and thickness several nm.

Kinetic Monte Carlo simulation of semiconductor quantum dot growth

Performing an event-based continuous kinetic Monte Carlo (KMC) simulation, We investigate the growth conditions which are important to form semiconductor quantum dot (QD) in molecular beam epitaxy (MBE) system. The simulation results provide a detailed characterization of the atomic kinetic effects. The KMC simulation is also used to explore the effects of periodic strain to the epitaxy growth of QD. The simulation results are in well qualitative agreement with experiments.

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

Homoepitaxial growth of 4H-SiC p(+)/pi/n(-) multi-epilayer on n(+) substrate and in-situ doping of p(+) and pi-epilayer have been achieved in the LPCVD system with SiH4+C2H4+H-2. The surface morphologies, homogeneities and doping concentrations of the n(-)-single-epilayers and the p(+)/pi/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 pi layer. The UV photodetectors fabricated on 4H-SiC p(+)/pi/n(-) multi-epilayers showed low dark current and high detectivity in the UV range.

Heavily doped polycrystalline 3C-SiC growth on SiO2/Si(100) substrates for resonator applications

3C-SiC is a promising material for the development of microelectromechanical systems (MEMS) applications in harsh environments. This paper presents the LPCVD growth of heavily nitrogen doped polycrystalline 3C-SiC films on Si wafers with 2.0 mu m-thick silicon dioxide (SiO2) films for resonator applications. The growth has been performed via chemical vapor deposition using SiH4 and C2H4 precursor gases with carrier gas of H-2 in a newly developed vertical CVD chamber. NH3 was used as n-type dopant. 3C-SiC films were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and room temperature Hall Effect measurements. It was shown that there is no voids at the interface between 3C-SiC and SiO2. Undoped 3C-SiC films show n-type conduction with resisitivity, Hall mobility, and carrier concentration at room temperature of about 0.56 Omega center dot cm, 54 cm(2)/Vs, and 2.0x 10(17) cm(-3), respectively. The heavily nitrogen doped polycrystalline 3C-SiC with the resisitivity of less than 10(-3) Omega center dot cm was obtained by in-situ doping. Polycrystalline SiC resonators have been fabricated preliminarily on these heavily doped SiC films with thickness of about 2 mu m. Resonant frequency of 49.1 KHz was obtained under atmospheric pressure.

Micro-raman investigation of defects in a 4H-SiC homoepilayer

Three types of defects, namely defect I, defect 11, defect 111, in the 4H-SiC homoepilayer were investigated by micro-raman scattering measurement. These defects all originate from a certain core and are composed of (1) a wavy tail region, (11) two long tails, the so called comet and (111) three plaits. It was found that there are 3C-SiC inclusions in the cores of defect 11 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 11 was formed. No inclusion was observed in the core of the defect I. The mechanisms of these defects are discussed.

The study of high temperature annealing of a-SiC : H films

A series of amorphous silicon carbide films were prepared by plasma enhanced chemical vapor deposition technique on (100) silicon wafers by using methane, silane, and hydrogen as reactive resources. A very thin (around 15 A) gold film was evaporated on the half area of the aSiC:H films to investigate the metal induced crystallization effect. Then the a-SiC:H films were annealed at 1100 degrees C for 1 hour in the nitrogen atmosphere. Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to analyze the microstructure, composition and surface morphology of the films. The influences of the high temperature annealing on the microstructure of a-SiC:H film and the metal induced metallization were investigated.

Photoluminescence and Raman scattering correlated study of boron-doped silicon nanowires

Boron-doped (B-doped) silicon nanowires (SiNWS) have been prepared and characterized by Raman scattering and photoluminescence (PL). B-doped SiNWS were grown by plasma enhanced chemical vapor deposition (PECVD), using diborane (B2H6) as the dopant gas. Raman spectra show a band at 480cm(-1),which is attributed to amorphous silicon. Photoluminescence at room temperature exhibits three distinct emission peaks at 1.34ev, 1.42ev, 1.47ev. Possible reason for these is suggested.

Characterization of polymorphous silicon thin film and solar cells

Polymorphous silicon (pm-Si:H) films have been prepared by a new regime of plasma enhanced chemical vapour deposition in the region adjacent of phase transition from amorphous to microcrystalline state. Comparing to the conventional amorphous silicon (a-Si:H), the pm-Si:H has higher photoconductivity (sigma(ph)), better stability, and a broader light spectral response range in the longer wavelength range. It can be found from Raman spectra that there is a notable improvement in the medium range order. There are a blue shift for the stretching mode of IR spectra and a red shift for the wagging mode. The shifts are attributed to the variation of the microstructure. By using pm-Si:H film as intrinsic layer, a p-i-n junction solar cell was prepared with the initial efficiency of 8.51% and a stabilized efficiency of 8.01% (AM1.5, 100mw/cm(2)) at room temperature (T-R).

Influence of the rapid thermal annealing on the properties of thin a-Si films

The variation of the structure, morphology and the electrical properties of thin amorphous silicon films caused by Rapid Thermal Annealing is studied. The films annealed at 1200degreesC for 2 minutes change their structure to polycrystalline and as a result their resistivity decreases by 4 orders of magnitude. Due to the small thickness of the as deposited amorphous silicon the obtained poly-Si is strongly irregular and has many discontinuities in its texture.

Defects in GaSb studied by coincidence Doppler broadening measurements

Undoped, Zn-doped and Te-doped GaSb with different concentrations were investigated by positron lifetime spectroscopy (PAS) and the Doppler broadening technique. Detection sensitivity of the latter technique was improved by using a second Ge-detector for the coincident detection of the second annihilation photon. PAS measurement indicated that there were vacancies in these samples. By combining the Doppler broadening measurements, the native acceptor defects in GaSb were identified to be predominantly Ga vacancy (V-Ga) related defects.

Long-wavelength SiGe/Si MQW resonant-cavity-enhanced photodiodes (RCE-PD)

Si1-xGex/Si optoelectronic devices are promising for the monolithic integration with silicon-based microelectronics. SiGe/Si MQW RCE-PD (Resonant-Cavity-Enhanced photodiodes) with different structures were investigated in this work. Design and fabrication of top- and bottom-incident RCE-PD, such as growth of SiGe MQW (Multiple Quantum Wells) on Si and SOI (Si on insulator) wafers, bonding between SiGe epitaxial wafer and SOR (Surface Optical Reflector) consisting Of SiO2/Si DBR (Distributed Bragg Reflector) films on Si, and performances of RCE-PD, were presented. The responsivity of 44mA/W at 1.314 mum and the FWHM of 6nm were obtained at bias of 10V. The highest external quantum efficiency measured in the investigation is 4.2%.

In situ doping of 3C-SiC grown on (0001) sapphire substrates by LPCVD

The heteroepitaxial growth of n-type and p-type 3C-SiC on (0001) sapphire substrates has been performed with a supply of SiH4+C2H4+H-2 system by introducing ammonia (NH3) and diborane (B2H6) precursors, respectively, into gas mixtures. Intentionally incorporated nitrogen impurity levels were affected by changing the Si/C ratio within the growth reactor. As an acceptor, boron can be added uniformly into the growing 3C-SiC epilayers. Nitrogen-doped 3C-SiC epilayers were n-type conduction, and boron-doped epilayers were p-type and probably heavily compensated.