J.M. Viner

Persistent photoconductivity in a-Si1−xSx:H at low sulfur concentration

Abstract We present the observation in homogeneous, unlayered a-Si 1−x S x :H alloys of a light-induced increase of the dark conductivity which is similar to that found in compensated and doping-modulated a-Si:H. This effect occurs for small sulfur concentrations. The excess conductivity can be annealed at about 200°C independent of the hydrogen concentration in the films.

Excitation of Er3+ ions in mixed amorphous-nanocrystalline GaN:Er films

We relate the strong enhancement of the Er 3 emission in amorphous + nanocrystalline GaN thin films alter annealing at 750°C with changes in the microstructure and respective changes in the electronic system. We use high resolution transmission electron microscopy (HRTEM), photothermal deflection spectroscopy and photoluminescence excitation measurements before and after annealing. The main results concern distinct resonant absorption bands of the Er 3+ ions superimposed on a broad background absorption from the amorphous matrix and very marked Stark splitting of the 4 F 92 absorption peak after optimal annealing.

A pulsed phase-sensitive technique for acoustical measurements

The pulsed phase-sensitive (PPS) technique for measurements of sound velocity and attenuation in fluids and solids is reviewed. With this technique, which uses a cycle-overlap principle, a time delay is measured between any two acoustical pulses transmitted through a sample or reflected from its boundaries. A current realization of the technique allows one to resolve the time-delay variation down to 0.1 ns. Thus at relative measurements with the PPS technique, precise sound velocity data can be obtained for samples of small thickness (about 1 mm). The technique is versatile and can also be used for accurate absolute measurements. The technique is most advantageous for studies of samples with high attenuation, in particular near phase transitions and at high temperatures. The technique also allows one to measure sound attenuation with moderate accuracy. An application of the technique that employs narrow-band radio frequency (rf) bursts for relative measurements of the phase sound velocity is considered in...

Tritium Induced Defects in Amorphous Silicon

We report the growth of tritium induced defects in tritium doped hydrogenated amorphous silicon (a-Si:H,T) as measured by electron spin resonance (ESR) and photothermal deflection spectroscopy (PDS). The measurements allow one to examine the accumulation of defects in a-Si:H,T where the defect production mechanism is known. Defects produced by tritium decay are found to be much less numerous than the number of decayed tritium atoms and they are metastable like Staebler-Wronski defects. These results provide new insight into the metastable defect creation and the role of hydrogen motion.

Microscopic origin of Er3+ emission in mixed amorphous-nanocrystalline Si:H films

Abstract ErO6 complexes, where every Er3+ ion is surrounded by six oxygen atoms forming an octahedron with C3v point symmetry are found to explain the strong Stark splitting of the characteristic Er3+ emission observed in the 1460–1610 nm range. An a-Si:H matrix serves as an ideal semiconductor host to permit co-doped O atoms to form an optimal ligand field around Er3+ ions.

Photoluminescence and electron spin resonance in nitrogen-rich amorphous silicon nitride

Abstract Electron spin resonance (ESR) and photoluminescence (PL) measurements have been employed to investigate some electronically important defects in nitrogen-rich amorphous silicon nitride films (a-SiNx:H where x > 1.3) prepared using plasma-enhanced chemical vapor deposition. The PL intensity decreases with time (fatigues) when excited with UV light. This fatigued PL can be restored (bleached) with the application of visible light. There exists an ESR signal in as-deposited films of a-SiNx:H which is temperature dependent. This ESR signal can be increased by irradiation with UV light, and the increased ESR signal can be bleached by application of visible light. Microscopic models for the defects responsible for these effects are discussed.

n‐type doping of amorphous silicon using tertiarybutylphosphine

The use of a liquid organic source for n‐type doping in hydrogenated amorphous silicon (a‐Si:H) is described. Tertiarybutylphosphine (TBP) vapor is added to silane in a rf glow discharge process to produce doped a‐Si:H thin films. Impurity levels from parts per million to about 1% phosphorus have been incorporated into the film with this method. Measurements of dark conductivity, photoconductivity, conductivity activation energy, electron spin resonance, and sub‐gap optical absorption of the TBP‐doped films are compared to those published for films doped with phosphine.

Photoluminescence in a‐Si:H and a‐Si1−xNx:H

In a‐Si:H photoluminescence (PL) has been measured as a function of the energy of excitation using excitation energies down to well below the optical gap. The relative quantum efficiency for PL at a specific energy increases as the excitation energy decreases. The results are interpreted in terms of a phonon assisted absorption mechanism. In a‐Si1−xNx:H the PL spectrum and the fatigue of the PL have been measured at 300 K. The possibility that the defect states in a‐Si1−xNx:H possess a negative effective electron‐electron correlation energy is critically examined.

On the nature of the paramagnetic defects in hydrogenated amorphous silicon nitride

Abstract ESR measurements in nitrogen-rich hydrogenated amorphous silicon nitride (a-SiN x :H with x > 1.3) as a function of temperature and microwave power reveal a second paramagnetic center in addition to the well-known, three-fold-coordinated silicon “dangling bond” (K center). This second center is a neutral, two-fold-coordinated nitrogen bonded to two silicon atoms (N 2 0 center). This discovery suggests that the dominant defects in a-SiN 1.6 :H are compensated K 3 + and N 2 − electron and hole traps, respectively.

Absorption in amorphous silicon doping-modulated multilayers

Abstract Photothermal deflection spectroscopy (PDS) measurements on doping-modulated multilayers of a-Si : H show that the measured width of the absorption due to band tails increases as the relative intrinsic layer thickness decreases. This increased width is due to a wider distribution of band tail states in the n- and p-doped layers. A large absorption (∼ 100 cm−1) well below the gap is observed in all samples.