Capacitance Deep-level Spectroscopy Research Articles

Spectroscopy of Technological Defects in Si Solar Cells by Analysis of Temperature Dependent Generation Currents

The efficiency of solar cells considerably depends on the technological defects introduced by the formation of junctions, passivation layers and electrodes. Identification of these defects present in the high conductivity base layer of modern solar cells by usage of the standard techniques, such as capacitance deep level spectroscopy, is restricted by extremely small size of samples with inherent enhanced leakage current on sample boundaries. Therefore, it is important to develop the alternative methods for the defect spectroscopy in the high conductivity junction structures, to directly control a relative low concentration of the technological defects. In this work, the spectroscopy of deep traps has been performed by combining the temperature scans of the thermal generation currents extracted from barrier capacitance charging transients and capacitance deep level transient spectroscopy techniques. The dominant carrier traps ascribed to the Cu and Ni impurities were revealed. DOI: http://dx.doi.org/10.5755/j01.ms.20.3.5194

Radiation defect distribution in silicon irradiated with 600 keV electrons

Low-doped n-type float zone silicon was irradiated with 600 keV electrons to fluences from 2×10 13 to 1×10 15 cm −2. Radiation defects, their introduction rates and full-depth profiles were measured by two complementary methods – the capacitance deep level spectroscopy and the high-voltage current transient spectroscopy. Results show that, in the vicinity of the anode junction, the profile of vacancy-related defect centers is strongly influenced by electric field and an excessive generation of vacancies. In the bulk, the slope of the profile can be derived from the distribution of absorbed dose taking into the account the threshold energy necessary for Frenkel pair formation and the dependency of the defect introduction rate on electron energy.

Optical Transient Current Spectroscopy of Deep Levels in Semi‐Insulating Indium Phosphide

Deep levels in iron‐compensated semi‐insulating were investigated by a form of digital optical transient current spectroscopy (OTCS). The decay of the transient photocurrent following periods of illumination was analyzed by a numerical method not previously applied to the problem. This could resolve a transient into a sum of exponential decays with time constants spanning a range of 104. Each time constant corresponds to the release of electrons or holes from a particular deep level. The temperature dependence gave information on the activation energy of the corresponding deep levels. By digitizing the entire transient, rather than recording two points, or their difference, as in the original OTCS method, only one sweep of temperature is required. Since the present algorithm determines the amplitudes and time constants of the exponential decays simultaneously, base‐line induced artifacts and related problems encountered in previous work are avoided. The temperature range was limited by excessive dark current above about 340 K, and by “negative transients” and low‐frequency oscillations below about 260 K. In the accessible range, nine deep levels were resolved. One level, previously unobserved in any type of , may be due to phosphorus vacancies. Of the remaining eight levels, one had previously been identified by OTCS in semi‐insulating . The remaining seven had not previously been detected in semi‐insulating but had activation energies close to levels previously found using capacitance deep level spectroscopy in doped (i.e., conducting) material. “Negative transients” are defined as transients in which the current initially undershoots the steady‐state value. Low frequency oscillations were observed in the same range of temperature, depending upon the applied voltage. It is tentatively proposed that a dependence on voltage of both positive and negative transients and of the low‐frequency oscillations arises from field‐enhanced trapping. The oscillations are attributed to traveling high‐field domains caused by hot‐electron trapping following the original Ridley model.