G. Ferenczi

Principles of the optimum lock-in averageing in DLTS measurement

The advantages of the transient capacitance/current signal averageing by lock-in amplifier are emphasized: improved signal to noise ratio and better detectability of non exponential transients. The concept of rate window independent phase setting is introduced which overcomes the existing difficulties of the lock-in detection technique. Finally, details of a custom built DLTS apparatus are given.

Dispersive microwave transient spectroscopy of deep levels in semiconductors

The detection of thermal emission of captured carriers from deep levels is still considered as the most sensitive way to derive informations on the electrically active impurities in semiconductors. To enhance the capabilities of probing thermal emission we are developing a microwave detection technique of this process. The present paper reports on the theoretical description and experimental verification of the functioning of the microwave detection system. The possibilities of this measurement technique in defect studies are illustrated on measurements of the Si:Se° system.

Identification of a deep electron trap in GaP:N

Abstract A deep electron trap in nitrogen doped GaP was studied. This trap is characterized by anisotropic electric field dependence, large lattice relaxation and recombination enhanced dissociation. The end product of the dissociation is substitutional nearest neighbour nitrogen pairs. A tentative model is suggested to identify this trap as split nitrogen interstitial pair.

DISPERSIVE MICROWAVE TRANSIENT SPECTROSCOPY OF DEEP LEVELS IN SEMICONDUCTORS

The detection of thermal emission of captured carriers from deep levels is still considered as the most sensitive way to derive informations on the electrically active impurities in semiconductors. To enhance the capabilities of probing thermal emission we are developing a microwave detection technique of this process. The present paper reports on the theoretical description and experimental verification of the functioning of the microwave detection system. The possibilities of this measurement technique in defect studies are illustrated on measurements of the Si:Se° system.

Deep level studies on traps showing non-exponential kinetics in GaAsP and GaP

DLTS and capacitance single-shot measurements were used to collect information on characteristically non-exponential levels in GaAsP and GaP. It is concluded that the non-exponentialities cannot be explained as collective phenomenon or the response of different independent deep levels. Using accurate single-shot capacitance decay data numerical curve fitting procedure showed thata)the actual trap concentration is underestimated by more than a factor of two if DLTS height is evaluated in the usual way:b)the trap activation energy is significantly overestimated as compared to the usual Arrhenius plot data if the effect of the inherent non-exponential thermal kinetics of these traps is not accounted for.

Reliability of LED’s; Are the accelerated ageing tests reliable?

The mechanisms leading to light output degradation of LED’s were studied using a number of different techniques, e.g. deep level spectroscopy, electroluminescence, minority carrier life time measurements. Several processes were revealed having different temperature and stress current dependence. Using these data extrapolations based on accelerated ageing test results are reexamined.

Surface corrosion as an apparent cause of degradation of GaP : N LED’s

The effect of heat treatment and subsequent current stressing was studied and compared on passivated and non-passivated VPE GaP∶N LED’s. It was found that the drastically increased degradation rate of the non-protected diodes is due completely to increased surface leakage current, no structural change or contamination of the semiconductor-bulk was observed.

Remarks on space-charge spectroscopy; An analysis on the temperature dependence of the junction capacitance

A detailed analysis of the temperature dependence of the small signal capacitance of reverse biasedp−n or metal-semiconductor junctions contains information on shallow and medium deep levels. It is argued that a simpleC(T) measurement gives unique information on shallow levels and indicates the choice of more elaborate space-charge method to detect deeper levels. The principles are illustrated on Au−nGaAsP Schottky barriers.