Lattice thermal conductivity of group-IV and III-V semiconductor alloys

The room-temperature thermal conductivity of semiconductor alloys is analyzed using a simplified model of the alloy-disorder scattering. Good agreement is achieved between the present model and published experimental data on various group-IV and III-V semiconductor alloys. A complete set of alloy-disorder parameters are estimated, which makes it possible to calculate the lattice thermal conductivity for optional composition of III-V semiconductor alloys, including III-N alloys. An ordering effect is also examined for the explanation of some intermetallic and semiconductor compounds like CuAu and SiC

Structural and photoluminescence properties of porous GaP formed by electrochemical etching

The structural and optical properties of porous GaP have been studied by scanning electron microscopy, spectroscopic ellipsometry, and photoluminescence (PL) spectroscopy. Porous GaP layers were fabricated by anodic etching in HF:H2O:C2H5OH=1:1:2 electrolyte on n-type (100) and (111)A substrates. The morphology of the porous GaP layer is found to depend strongly on the surface orientation. Apart from the red emission band at ～1.7 eV, a supra-band-gap (EgX) emission has been clearly observed on the porous GaP (111)A sample. The anodic porous layer on the (100) substrate, on the other hand, has shown only the red emission at 300 K and both red and green donor-acceptor pair emissions at low temperatures. The correlation between the PL properties and the porous morphology is discussed. An optical transition model is also proposed for the explanation of the PL emission properties of the porous GaP samples

Spectroscopic investigation of light-emitting porous silicon photoetched in aqueous HF/I2 solution

The optical properties of porous silicon (PSi) photoetched in aqueous HF/I2 solution are investigated using spectroellipsomety (SE), electroreflectance (ER), photovoltage (PV), photoconductivity (PC), photoluminescence (PL), and Fourier transform infrared (FTIR) spectroscopy. The PSi layers were formed in a HF/I2 solution on n-Si substrates under Xe lamp illumination. The SE ε(E) and related data show an interference oscillation in the region below E～3 eV, where the PSi material is nearly transparent. The PV and PC spectra reveal three individual peaks A, B, and C at ～1.2, ～1.7, and ～2.5 eV, respectively, arising from the PSi layer itself. Peak C is also observed in the ER spectrum, together with a broadened E1 peak at ～3.4 eV. Change in the fundamental-absorption-edge nature (EgX) from the indirect gap in crystalline silicon to the quasidirect gap in PSi is found in the PV and PC spectra. The PL spectrum shows a broad peak at ～2.0 eV(B). Peaks A, B, and C observed in the PSi layer may originate from the nondirect optical transitions at and above the lowest absorption edges EgX (A and B) and EgL (C). The quantum-mechanical size effect, i.e., a relaxation of the momentum conservation, makes possible the nondirect or quasidirect transitions at and above EgX and EgL in porous materials. The FTIR data support that the PL emission is due to the surface-sensitive quantum confinement effect

Strong and stable ultraviolet emission from porous silicon prepared by photoetching in aqueous KF solution

A new method of fabricating porous silicon emitting in the ultraviolet (UV) spectral region is presented. This method uses photoetching in an aqueous salt (KF) solution. Strong UV photoluminescence is observed at ～3.3 eV with a full width at a half maximum of ～0.1 eV, which is much narrower than those reported previously. Fourier transform infrared spectroscopy suggests that the surface oxide produced during photoetching plays an important role in the UV emission of the KF-prepared PSi

Properties of GaP(001) surfaces chemically treated in NH4OH solution

Chemically cleaned GaP(001) surfaces in 25% NH4OH solution have been studied using spectroscopic ellipsometry (SE), ex situ atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and wettability measurement techniques. The SE data clearly indicate that the solution causes removal of the native oxide film immediately upon immersing the sample. The SE data also indicate that when the native oxide film is completely etch removed, the resulting surface is still roughened. The estimated roughness thickness is ～1.2 nm, in excellent agreement with the AFM rms value (～1.2 nm). The XPS spectra confirm the removal of the native oxide from the GaP surface. The XPS data also suggest a thin oxide overlayer, ～0.3 nm thick, on the etch-cleaned GaP surface. The wettability measurements indicate that the as-degreased surface is hydrophobic, while the NH4OH-cleaned surface is hydrophilic. This result is in direct contrast to those obtained from acid cleaned surfaces, which are usually hydrophobic. The origin of hydrophilicity may be singular and associated hydroxyl groups bonded on the GaP surface

Properties of GaP(001) surfaces treated in aqueous HF solutions

Chemically cleaned GaP(001) surfaces in aqueous HF solutions have been studied using spectroscopic ellipsometry (SE), ex situ atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), wettability, and photoluminescence (PL) measurements. The SE data clearly indicate that the solutions cause removal of the native oxide film immediately upon immersing the sample (?1 min). The SE data, however, suggest that the native oxide film cannot be completely etch-removed. This is due to the fact that as soon as the etched sample is exposed to air, the oxide starts to regrow. The SE estimated roughness is ～1 nm, while the AFM roughness value is ～0.3 nm. The XPS spectra confirm the removal of the native oxide and also the presence of regrown oxide on the HF-etched GaP surface. The wettability measurements indicate that the HF-cleaned surface is hydrophobic, which is in direct contrast to those obtained from alkaline-cleaned surfaces (hydrophilic). A slight increase in the PL intensity is also observed after etching in aqueous HF solutions

Optical absorption and photoluminescence in the ternary chalcopyrite semiconductor AgInSe2

Optical-absorption and photoluminescence (PL) spectra have been measured on the ternary chalcopyrite semiconductor AgInSe2 at T=13–300 K. The direct-band-gap energy Eg of AgInSe2 determined from the optical absorption measurements shows unusual temperature dependence at low temperatures. The resultant temperature coefficient ?Eg/?Tis found to be positive at T <125 K and negative above 125 K. The PL spectra show asymmetric emission bands peaking at ～1.18 and ～1.20 eV at T=13 K, which are attributed to donor-acceptor pair recombinations between exponentially tailed donor states and acceptor levels. An energy-band scheme has been proposed for the explanation of the peculiar PL emission spectra observed in AgInSe2

Properties of light-emitting porous silicon photoetched in aqueous HF/FeCl3 solution

The formation of yellow-light-emitting porous silicon (PSi) layers in a HF solution with adding an oxidizing agent FeCl3 is presented. The PSi layers are formed by photoetching under Xe lamp illumination. The photoluminescence (PL) intensity is strongly dependent on the FeCl3 concentration and shows a maximum at x~25 wt % [50 wt % HF:(x wt % FeCl3 in H2O)=1:1]. The surface topography as characterized by atomic force microscopy reveals features on the order of 20-100 nm with a root-mean-squares roughness of =20 wt %). The PSi formation mechanism can be explained with the aid of a surface energy-band diagram of n-type silicon in the HF/FeCl3 electrolyte

Spectroscopic characterization of naturally and chemically oxidized silicon surfaces

We have determined the thicknesses of naturally and chemically grown oxides on HF-cleaned silicon surfaces in ambient air and in NH4OH/H2O2/H2O solution, respectively, using spectroscopic ellipsometry. The naturally grown oxide thickness versus air-exposure time plots yield a rate constant of 3.5+-0.5 Å/decade in ambient air. Chemical oxidation occurs immediately upon immersing the sample in the chemical solution and leaves the sample surface terminated with ～6 Å of a chemical oxide. Photoreflectance intensity is found to be strongly dependent on such surface processing, and results are explained by the different degree of surface (interface) states

Ultraviolet emission from porous silicon photosynthesized in aqueous alkali fluoride solutions

Stable ultraviolet (UV) photoluminescence (PL) has been observed at room temperature in porous silicon (PSi) fabricated by photoetching in aqueous alkali fluoride solutions. The aqueous solutions used are 1 M NaF and 1 M KF.They give an alkaline reaction caused by partial hydrolysis. The PL peaks at ～3.3 eV have a full width at half maximum of ～0.1 eV, which is much smaller than those reported previously (?0.5 eV). Spectral analyses suggest that both quantum confinement and surface passivation effects enable the observation of UV emission in NaF- and KF-prepared PSi samples