Jorg Versluys

DLTS and admittance measurements on CdS/CdTe solar cells

Abstract Deep level states can affect the characteristics of thin film solar cells both by their charge and by their recombination. Hence, full solar cell characterisation should include deep states. Deep level transient spectroscopy (DLTS) and admittance spectroscopy (AS) measurements ( Y ( f , T )) have been made on a series of CdTe/CdS thin film solar cells. Majority and minority trap DLTS was performed between 5 and 330 K revealing semi-shallow to mid-gap traps, depending on the sample. The DLTS results are compared with those of AS in the 100–320 K range at frequencies from 100 Hz to 1 MHz. The energy range probed with the AS is narrower than that of the DLTS method. Both methods give comparable results in the energy range where they overlap. The results are compared with literature data. The difference between cells which received a CdCl 2 treatment in air and those which received the treatment in vacuum is discussed.

Photoluminescent and structural properties of CaS:Pb electron beam deposited thin films

The structural and optical properties of electron beam deposited CaS:Pb thin films were investigated as a function of annealing temperature and lead concentration. X-ray diffraction measurements show weak crystallinity for such layers. Although this improves with higher annealing temperatures, no difference in the grain size could be seen by means of atomic force microscopy. This can be explained by columnar growth or relaxation of strain. At high annealing temperatures (1000 °C for 2 min) and sufficiently high lead concentrations (0.74 at%), a bright blue photoluminescence could be observed. Excitation spectra were acquired showing different excitation bands.

Impact of Direct Plasma Hydrogenation on Thermal Donor Formation in n-Type CZ Silicon

Institut de Microelectro`nica de Barcelona, Campus UAB, 08193 Bellaterra, SpainIn this paper, the role of a direct plasma hydrogenation treatment and a subsequent air annealing at 450°C in the formation ofthermal donors ~TDs! in n-type Czochralski~CZ! silicon is investigated by means of a combination of capacitance-voltage~C-V!and deep-level transient spectroscopy~DLTS!. The hydrogenation treatment is found to enhance the introduction rate of TDs at450°C for shorter annealing times, reaching its maximum acceleration after5handforthelongest plasma hydrogenation studied~2h!. For much longer annealing times, the TD introduction rate becomes independent of the presence of hydrogen in the material.DLTS detects only one donor level having an activation energy, which lowers with increasing doping density of the material, from0.106 to 0.093 eV. After activation energy correction for the Poole-Frenkel electric-field-enhanced emission, this trap is found tofit well with the conventional singly ionized oxygen thermal donor level. However, from C-V free carrier and DLTS trapconcentrations, it is derived that other shallower donors, created by the plasma hydrogenation and 450°C anneal should play animportant role in the free carrier concentration increase of the n-CZ silicon.© 2004 The Electrochemical Society. @DOI: 10.1149/1.1824039# All rights reserved.Manuscript submitted March 14, 2004; revised manuscript received May 5, 2004. Available electronically November 17, 2004.

Microoptical characterization of electroluminescent SrS:Cu,Ag thin films by photo- and cathodoluminescence observations

For SrS:Cu,Ag thin film phosphors, a postdeposition annealing step is imperative in order to obtain bright photo- or electroluminescence. However, it is not clear to date what is the most important effect of this treatment, a recrystallization of the host lattice or a redistribution of the activators. The present article discusses the microscopic emission characteristics of annealed photoluminescent layers SrS:Cu,Ag. Using cathodoluminescence measurements, it is shown that emission, originating from the grain boundaries, is very weak compared to the emission from the bulk of the grains.

DLTS study on deep levels formed in plasma hydrogenated and subsequently annealed silicon

P-n junctions are created in p-type Czochralski silicon after a low temperature (270°C) hydrogen plasma exposure. This is attributed to the formation of hydrogen-related shallow donors. A deep level (E1) with an activation energy of about EC-0.12 eV is observed by DLTS measurement and assigned to a metastable state of the hydrogen-related shallow donors. At an annealing temperature of 340°C, the E1 centres disappear and oxygen thermal donors appear. The concentrations of the oxygen thermal donors are found typically to be 2-3 decades lower than that required for over-compensating the initial p-type doping and for contributing the excess free carriers.

Deep levels in high-temperature 1 MeV electron irradiated n-type czochralski silicon

This work describes the radiation defects formed in high-temperature (450°C) 1 MeV electron-irradiated n-type Czochralski (Cz) silicon. A dedicated irradiation configuration has been used, which relies on sample heating by the energy deposited by the electron beam current. It is shown that the vacancy oxygen (VO) or A center is the dominant radiation defect under these circumstances. In addition, a whole series of unknown deep electron traps is reported, whose trap parameters (activation energy, electron capture cross section) depend, among other factors, on the starting interstitial oxygen concentration. It is speculated that their origin is related to complexes of oxygen and vacancies.

P-N Junction Diodes Fabricated Based on Donor Formation in Plasma Hydrogenated P-Type Czochralski Silicon

A rather large amount of shallow donors is created in p-type Czochralski silicon (Cz Si) wafers after a hydrogen plasma exposure at ∼270 °C (substrate temperature) and a subsequent annealing in the temperature range of 350-450 °C. This two-step process has been used for the fabrication p-n junction diodes at low temperatures. Current-voltage characteristics show that the breakdown voltages of these diodes are higher than 100 V. The diode leakage is found to be improved after slow ramp annealing at temperatures up to 250 °C. Deep level transient spectroscopy measurements reveal that the oxygen related thermal donor is not the dominant doping species as expected before.