Photoassisted Kelvin Probe Force Microscopy on Multicrystalline Si Solar Cell Materials

Abstract

Precise etch depth control of ultra-thin HfO 2 (3.5 nm) films applied as a gate oxide material was investigated by using atomic layer etching (ALET) with an energetic Ar beam and BCl 3 gas. A monolayer etching condition of 1.2 Å/cycle with a low surface roughness and an unchanged surface composition was observed for ultra-thin, ALET-etched HfO 2 by supplying BCl 3 gas and an Ar beam at higher levels than the critical pressure and dose, respectively. When HfO 2 -nMOSFET devices were fabricated by ALET, a 70% increase in the drain current and a lower leakage current were observed compared with the device fabricated by conventional reactive ion etching, which was attributed to the decreased structural and electrical damage.

Photovoltage decay processes in Cu(In, Ga)Se<inf>2</inf> solar cells studied by photo-assisted Kelvin probe force microscopy

“…The Ga content in the CIGS absorption layer in those samples was varied in a range between 0.23 and 0.50. Our P-KFM system is based on a commercial AFM system (SPI4000/SPA300HV, Hitachi High-Tech Science Corp., Japan) combined with some external electronics and light sources to obtain accurate surface potential values and photovoltages [2][5], as schematically illustrated in Fig. 1.…”

“…In addition, the CIGS solar cell typically has a multilayered structure which should includes potential barriers at the heterointerfaces, and therefore we have to care about the possibilities of the disturbance of the carrier transport across those barriers and the consequent increase of an internal resistance in the solar cell. In this study, we have performed photo-assisted Kelvin probe force microscopy (P-KFM), which we originally proposed [2], on the CIGS solar cells to investigate carrier recombination process through evaluations of a time constant  for photovoltage decay, which is considered to represent a time constant required for the carrier transport across the potential barriers at the hetero-interfaces in the cell structure, and a contribution ratio r of fast carrier recombination process in the entire recombination processes [3] [4].…”

Photovoltage decay measurements on Cu(In,Ga)Se<inf>2</inf> solar cells by photo-assisted Kelvin probe force microscopy

“…Our P-KFM system consists of a commercial AFM system (SPI4000/SPA300HV, SII NanoTechnology Inc., Japan) combined with some external electronics and light sources to obtain accurate surface potential values and photovoltages (SPVs) [3][5]. The system is illustrated schematically in Fig.…”

“…For the photovoltage decay measurements, on the other hand, the incident light is modulated by an acousto-optic modulator (AOM) as shown in Fig. 1, and the temporally-averaged photovoltages were measured at various modulation frequencies [2] [3].…”

An investigation of band profile around the grain boundary of Cu(InGa)Se2 solar cell material by scanning probe microscopy

“…In the present study, we have adopted two scanning probe methods with high spatial resolution to investigate the band profiles around the GBs of CIGS materials. One of these is scanning tunneling spectroscopy (STS) based on scanning tunneling microscopy (STM), and the other is Kelvin probe force microscopy (KFM) carried out under light illumination, which is a technique of our own devising, called photo‐assisted KFM (P‐KFM) . The STS method enables us to evaluate the band gap values in the semi‐conductor materials, whereas the distribution of the conduction band edge is estimated from the surface potential measured by the P‐KFM method.…”