Radio Frequency Nitrogen Plasma Source Research Articles

The (3 × 3) reconstruction and its evolution during the nitridation of GaAs(001)

Nitridation of GaAs(001) was performed using a radio frequency nitrogen plasma source in a molecular beam epitaxy chamber. The nitrogen-induced GaAs(001) (3 × 3) reconstruction was investigated by reflection high energy electron diffraction (RHEED) and X-ray photoemission spectroscopy (XPS). The temperature dependence of the (3 × 3) reconstruction as well as its evolution during further nitridation was observed by RHEED; we found that the (3 × 3) reconstruction could be obtained in the temperature range 400–580 °C by a very low dose of atomic nitrogen deposition. The nitrogen coverage in the (3 × 3) reconstruction is determined to be in the range 0.2–0.4 ML using XPS. We also discuss the atomic model of the (3 × 3) reconstruction and the energetics of its formation and stability.

Effect of Buffer Layer and III/V Ratio on the Surface Morphology of Gan Grown by MBE

The surface morphology of GaN is observed by atomic force microscopy for growth on GaN and AlN buffer layers and as a function of III/V flux ratio. Films are grown on sapphire substrates by molecular beam epitaxy using a radio frequency nitrogen plasma source. Growth using GaN buffer layers leads to N-polar films, with surfaces strongly dependent on the flux conditions used. Flat surfaces can be obtained by growing as Ga-rich as possible, although Ga droplets tend to form. Ga-polar films can be grown on AlN buffer layers, with the surface morphology determined by the conditions of buffer layer deposition as well as the III/V ratio for growth of the GaN layer. Near-stoichiometric buffer layer growth conditions appear to support the flattest surfaces in this case. Three defect types are typically observed in GaN films on AlN buffers, including large and small pits and “loop” defects. It is possible to produce surfaces free from large pit defects by growing thicker films under more Ga-rich conditions. In such cases the surface roughness can be reduced to less than 1 nm RMS.

Epitaxial growth of n- and p-type ZnCdSe on InP

Chlorine doping and nitrogen doping of lattice-matched ZnCdSe on InP were investigated. High-quality ZnCdSe films were successfully grown on a GaInAs buffer layer using a dual-growth-chamber molecular-beam epitaxy system. The reflection high-energy diffraction oscillations on the ZnCdSe surface persisted for about 80 periods after the ZnCdSe layer growth was started. The full-width at half-maximum of the double-crystal X-ray (0 0 4) diffraction curve was as narrow as 42 arcsec. Epitaxial chlorine doping and epitaxial nitrogen doping were performed using ZnCl 2 and a radio-frequency nitrogen-plasma source, respectively. In the ZnCdSe: Cl layer, free-electron concentrations up to 7×10 18cm −3 were obtained. In the ZnCdSe: N layer, p-type conductivity was observed for the first time with a maximum net acceptor concentration of 3.5 × 10 16 cm −3.

Effect of Buffer Layer and III/V Ratio on the Surface Morphology of Gan Grown by MBE

AbstractThe surface morphology of GaN is observed by atomic force microscopy for growth on GaN and AlN buffer layers and as a function of III/V flux ratio. Films are grown on sapphire substrates by molecular beam epitaxy using a radio frequency nitrogen plasma source. Growth using GaN buffer layers leads to N-polar films, with surfaces strongly dependent on the flux conditions used. Flat surfaces can be obtained by growing as Ga-rich as possible, although Ga droplets tend to form. Ga-polar films can be grown on AlN buffer layers, with the surface morphology determined by the conditions of buffer layer deposition as well as the III/V ratio for growth of the GaN layer. Near-stoichiometric buffer layer growth conditions appear to support the flattest surfaces in this case. Three defect types are typically observed in GaN films on AlN buffers, including large and small pits and “loop” defects. It is possible to produce surfaces free from large pit defects by growing thicker films under more Ga-rich conditions. In such cases the surface roughness can be reduced to less than l nm RMS.

Growth and p-type doping of GaN on c-plane sapphire by nitrogen plasma-assisted molecular beam epitaxy

Effect of III/V ratio on the quality of GaN epilayers has been investigated. GaN films were grown on the c-plane of sapphire by using radio frequency (RF) nitrogen plasma-assisted molecular beam epitaxy (MBE). A home-made III-V nitride MBE system consisted of an inductively coupled RF nitrogen plasma source and solid source effusion cells were used to grow GaN films. The results of reflection high energy electron beam diffraction (RHEED) and double crystal X-ray diffraction indicate that crystal quality of GaN epilayers is strongly dependent on the Ga flux. Room temperature photoluminescence spectrum of undoped GaN epilayer is peaked at 3.39 eV and no discernible yellow luminescence resulting from ion damages are observed. Effect of Mg flux on the carrier concentration of p-GaN have also been investigated. Fairly uniform p-doping concentration as high as 5.33 x 10 18 /cm 3 throughout the GaN crystal were obtained. The sample grown with T Ga = 900°C and T Mg = 130°C exhibits very streaky RHEED patterns and the highest p-type doping concentration.

Optical characteristics of p-type GaN films grown by plasma-assisted molecular beam epitaxy

Using a molecular beam epitaxy system equipped with an inductively coupled radio frequency nitrogen plasma source, p-type GaN films were grown on sapphire substrates with no postgrowth treatment. Uniformity of the surface morphology and spatial homogeneity of the luminescence of the films were investigated using scanning electron microscopy and cathodoluminescence (CL) imaging, respectively. By examining the dependence of photoluminescence on the excitation laser power density at 6 and 300 K, three different emissions having different origins were identified. A blue emission at ∼3.25 eV is associated with shallow Mg impurities, while two different lower-energy emissions at ∼2.43 and ∼2.87 eV are associated with deep Mg complexes. The spatial distributions of the shallow and deep Mg impurities dominating the optical properties of the p-type GaN films were also examined along the growth direction by low- and room-temperature CL using an electron beam with a range of penetration depths

Atomic nitrogen production in nitrogen-plasma sources used for the growth of ZnSe : N and related alloys by molecular-beam epitaxy

A high resolution study of the optical emission from nitrogen-plasmas produced by an Oxford Applied Research radio frequency plasma source is reported. Strong atomic emission lines in the near-infrared spectral region provide unequivocal evidence that the nitrogen-plasma source generates an appreciable flux of nitrogen atoms. Nitrogen atoms, rather than N 2 molecules in the plasma, are the most likely nitrogen-plasma species responsible for the successful p-type doping of ZnSe : N and related alloys. Emission spectra from the radio frequency nitrogen-plasma source are compared with similar emission spectra obtained from an electron cyclotron resonance microwave nitrogen-plasma source.