Bernard J. Feldman

Structural and optical properties of amorphous carbon nitride

Amorphous carbon nitride thin films have been grown by plasma decomposition of a feedstock of CH4 and N2. In the films with higher nitrogen concentration, the infrared absorption spectra are dominated by NH2 modes and give strong evidence of a polymeric structure. The optical absorption and photoluminescence spectra show that nitrogen incorporation decreases the bandgap and increases the structural order of these thin films.

Low defect density CdTe(111)‐GaAs(001) heterostructures by molecular beam epitaxy

(111) oriented CdTe has been grown on (001) oriented GaAs substrates by molecular beam epitaxy. Double crystal x‐ray diffraction rocking curve and photoluminescence measurements indicate that the CdTe is of exceptional quality despite the large lattice mismatch of 14.6%.

Room‐temperature photoluminescence in spray‐pyrolyzed CdS

Very intense room‐temperature photoluminescence has been observed near 1000 nm in CdS films prepared by spray pyrolysis. Since this material can be easily fabricated into p‐n devices, this suggests the possibility of inexpensive electro‐optical devices. Also, the photoluminescence spectra of CdS and amorphous Si:H are very similar.

Thermalization Gap Excitation Photoluminescence and Optical Absorption in Amorphous Silicon-Hydrogen Alloys

Abstract We report the photoluminescence spectra of amorphous silicon-hydrogen alloys excited by 1.68 eV to 2.07 eV photons. The spectrum excited by 1.68 eV photons is dramatically shifted to the red, which we interpret in terms of holes photoexcited above a “thermalization gap.” In an attempt to be quantitative, we construct a simple model for the photoluminescence process which gives results consistent with our data and a “thermalization gap” of approximately 1.60 eV. These results further our understanding of the electronic states and the photoluminescence process in this material. We extend this model to calculate the optical absorption of this material and find the calculation in good agreement with experimental data, giving us an estimate of the valence band density of states in the band gap.

Microhardness study of amorphous hydrogenated boron carbide deposited on a cathode substrate by plasma deposition

We have grown amorphous hydrogenated boron carbide thin films on a cathode substrate by rf plasma decomposition of diborane and methane. The chemical composition, infrared absorption, optical absorption, microhardness, and adhesion of these thin films were measured. As a function of increasing diborane concentration in the feedstock, we observe increasing boron and decreasing hydrogen concentrations, increasing infrared absorption at 1300 cm−1 due to boron icosahedra, increasing optical band gaps, dramatically increased microhardness, and increased adhesion to the underlying substrates of these thin films. These results provide evidence that the presence of boron icosahedra increases microhardness, adhesion, and optical band gaps.

Electrical and electron spin resonance measurements of amorphous hydrogenated carbon nitride

Abstract The electrical conductivity and electron spin resonance spectra of amorphous hydrogenated carbon nitride and amorphous hydrogenated carbon are reported. Both measurements present evidence that the addition of nitrogen significantly decreases the density of dangling bonds, similar to the role of hydrogen in amorphous hudrogenated silicon. These results are also consistent with previously reported optical absorption and photoluminescence measurements.

Photoluminescence in spray‐pyrolyzed CdTe

We report very intense photoluminescence in spray‐pyrolyzed CdTe at 77 K. We also notice striking similarities in the luminescence spectra, decay, and temperature dependence between CdTe and other thin‐film semiconductors, which we interpret in terms of recombination at defect sites in intergranular regions.

13C NMR spectroscopy of amorphous hydrogenated carbon nitride

Abstract The 13 C NMR spectra of chemical vapor deposited amorphous hydrogenated carbon nitride thin films were measured and a number of sharp lines superimposed on top of a broad peak were observed. These sharp lines have been interpreted as arising from nanocrystals of nitrogen-containing aromatic rings terminated by amino groups. The concentration of these nanocrystals increases with increasing nitrogen concentration and decreases with thermal annealing. These nanocrystals are responsible for the increased structural order in these films. Similar nanocrystals are probably present in sputtered carbon nitride thin films. There is no 13 C NMR evidence of any phase of crystalline carbon nitride in either the chemical vapor deposited or sputtered films.

Photoluminescence in liquid phase epitaxially grown Hg0.3Cd0.7Te

The photoluminescence spectra of liquid phase epitaxially (LPE) grown Hg0.3Cd0.7Te and its CdTe substrate have been measured. The CdTe spectra consist of two band‐edge sets of lines, B and C, while the Hg0.3Cd0.7Te spectra consist of one set of lines, A. From the temperature dependence of both the integrated intensity and peak position, we determined that the A line is unrelated to the C line but is very possibly related to the B line. The B line in CdTe is due to recombination of electrons and holes bound to a neutral donor. This suggests that the same neutral donor may be present in both materials, whereas the impurity or defect responsible for the C line in CdTe is undetectable in LPE‐grown Hg0.3Cd0.7Te.

Amorphous hydrogenated carbon from the plasma deposition of C2H2, C2H4 or CH4

Abstract The growth of amorphous hydrogenated carbon (a-C : H) from the plasma deposition of C2H2, C2H4, or CH4 is reported. Measurements of the infrared absorption spectra, the optical gaps, and the photoluminescence spectra of these thin films are compared with each other, to those on a-C : H by previous workers, and to those on a-Si : C. The possibility of an a-C : H/a-Si : H hetero-junction solar cell is suggested.