Full band structure calculation of minority carrier lifetimes in HgCdTe and thallium-based alloys

We have calculated the full band structures-based minority carrier lifetimes in small-gap semiconductor alloys. The contribution from first-order Coulomb interactions and second-order electron-electron interactions coupled through optical phonons are included. Our results agree reasonably well with experiments in Hg_0.78Cd_0.22Te. Similar calculations were carried out for lifetimes in In_0.67Tl_0.33P, In_0.85Tl_0.15As, and In_0.92Tl_0.08Sb. The minority carrier lifetimes in In_0.67Tl_0.33P and In_0.92Tl_0.08Sb are shorter than that in Hg_0.78Cd_0.22Te at all temperatures. However, the low-temperature minority carrier lifetime in In_0.85Tl_0.15 As is an order of magnitude longer than that in Hg_0.78Cd_0.22Te. Our calculations further suggest the possibility of increasing the lifetimes of minority carriers either by decreasing the density of states inside a critical energy and momentum region or by increasing the total hole population outside that critical region. Experimental observations that substantiate this suggestion are discussed.     

Experimental characterization and numerical analysis of the 4H-SiC p-i-n diodes static and transient behaviour

Steady-state and turn-off switching characteristics of aluminium-implanted 4H-SiC p-i-n diodes designed for high-current density operation, are investigated experimentally and by mean of numerical simulations in the 298-523 K temperature range. The diodes present circular structure with a diameter of 350 μm and employ an anode region with an aluminium depth profile peaking at 6×10¹⁹ cm⁻³ at the surface. The profile edge and the junction depth are located at 0.2 and 1.35 μm, respectively. At room temperature the measured forward current density is close to 370 A/cm² at 5 V with an ideality factor always less than 2 before high-current injection or device-series resistance became dominant. The transient analysis reveals a strong potential of this diodes for use in high-speed, high-power applications, especially at high temperature, with a very low turn-off recovery time (<80 ns) in the whole range of test conditions. The simulated results match the experimental data, showing that the switching performance is mainly due to the poor minority charge carrier lifetime estimated to be 15 ns for these implanted devices.     

Imaging Surface Pits and Dislocations in 4H-SiC by Forescattered Electron Detection and Photoluminescence

Forescattered electron detection (FED) was utilized to image surface depressions resulting from threading screw and edge dislocations in 4H-SiC epitaxial layers. These surface depressions, or growth pits, exhibited two morphology types. Screw and edge dislocations could be imaged by photoluminescence and differentiated by their interactions with propagating partial dislocations (PDs). Correlations between FED and photoluminescence showed that sharp-apex pits 1 μm in size and strip-shaped pits 500 nm in size could be linked to individual screw and edge dislocations, respectively. Forescattered electron detection demonstrated sufficient sensitivity to image surface features previously resolvable only by atomic force microscopy. This new technique is nondestructive, noncontact, and capable of rapid, spatial mapping of growth pits resulting from threading screw and edge dislocations in SiC epitaxial layers.