We studied the photoconductivity responses in amorphous In-Ga-Zn-O (a-IGZO) films using a time-resolved microwave photoconductivity decay (μ-PCD) technique. The a-IGZO film characteristics are correlated with three components in the photoconductivity response: the peak value and two decay constants. The peak value originated from the density of the photo-generated free carriers through carrier generation and recombination processes during laser pulse irradiation. Power law characteristics indicated that the peak values are attributed to recombination process related to the exponential distribution of the conduction band tail states. After the laser pulse was turned off, the reflectivity signal decreased rapidly, indicating fast recombination of the photo-generated carriers. This fast decay component is suggested to be related to the recombination processes through the deep level states. Following the fast decay, a slow decay with a decay constant on the order of microseconds appeared. This slow decay was attributed to the reemission of trapped carriers with an activation energy of ∼0.2 eV. In addition, both the fast and slow decays for the wet annealed a-IGZO film were longer than those of the as-deposited a-IGZO film. The decay constants are considered to reflect the density of the subgap states that act as trapping or recombination centers. The μ-PCD method provides a useful estimation of the film quality, such as the density of the defect states, and the physical properties of electronic devices using a-IGZO films.

The film quality of amorphous In–Ga–Zn–O (a-IGZO), an amorphous oxide semiconductor (AOS), was studied by the microwave photoconductivity decay (μ-PCD) method. Also, μ-PCD mappings over a 6 in. wafer were undertaken. It was found that the peak signal of the decay curve had a strong correlation with the a-IGZO transistor performance and hence the film quality. The film annealed under a wet condition showed the highest mobility and had the highest peak signal. The μ-PCD method was found to be a very useful tool to evaluate the film quality and predict the performance of AOS transistors fabricated under different process conditions.

Excess carrier lifetime in bulk 2-in. SiC wafers was measured by microwave photoconductivity decay (µ-PCD). The mapping technique was used to obtain the lifetime distribution in the entire wafer. We observed the birefringence image and X-ray topograph of the wafers in order to determine the structural defect distribution, and the net donor concentration distribution was also observed by capacitance–voltage measurements. By comparison of lifetime maps with the structural defect distribution, it was found that relatively long lifetime regions correspond to regions with high-density structural defects. The net donor concentration did not show a clear influence on the carrier lifetimes. We confirmed that surface recombination has a negligible effect on the carrier lifetimes, and therefore the lifetimes obtained from mapping measurements are mainly dominated by carrier recombination behavior in the bulk of the wafers.

The asymptotic spherical aberration and distortion coefficients of electron lenses always depend upon the position of the object, or the magnification, in a very simple way, and furthermore the quantities that specify the distortion are closely related to those giving the spherical aberration. These relationships are set out, and numerical values of the coefficients concerned are tabulated for Glaser's bell-shaped model; both the symmetric and the asymmetric bell are considered, and the effect of scaling with respect to the minimum projector focal length is investigated.

Highly sensitive lifetime mapping equipment using the UV laser excited differential microwave photoconductivity decay technique was developed to observe the defect and contamination distribution in ultrathin silicon-on-insulator ͑SOI͒ layers. The technique was successively applied to the evaluation of state-of-the-art SOI wafers. Through theoretical analysis, it was quantitatively confirmed that the lifetime is shortened as the SOI film becomes thin, due to an increase in interface recombination. The large improvement in sensitivity attained by the differential detection enabled us to evaluate nonuniformities in the active layer quality by overcoming the difficulty of detection normally experienced by the decrease in the thickness of the SOI layer. Using light illumination with an extremely short penetration depth and the barrier effect of the buried oxide layer, it was found that the generated carriers were confined to the active layer, and lifetime data reflecting the quality of the SOI layer could be obtained. In the lifetime map for an SOI layer with a thickness of 52 nm, numerous islandlike spots with long lifetime, which were believed to be caused by HF defects or thin silicon areas, were detected.