Regions Of Low Efficiency Research Articles

Striped anode engineering: a concept for fast switching power devices

In this paper, the striped anode concept is evaluated, for the first time in a MOS controlled power device, as a method of controlling the anode injection efficiency and enhancing of the turn-off performance. Simulation results using a 2d-mixed mode device-circuit system indicate that rather than having a blanket implanted anode, a striped anode structure can result in a significantly improved trade-off between turn-off energy losses and the on-state voltage drop. It is shown that when applied to the 6.5 kV IGBT, the improvement can be more than a factor of two when switching 30 A cm −2, in comparison to conventional uniform lifetime control. A striped anode structure consists of high injection regions (p + stripes), sandwiched between thin lightly doped p − regions of low injection efficiency. The p + stripes provide an optimum level of conductivity modulation required for a given on-state voltage drop in the N-drift region of a planar IGBT, while the low efficiency regions accelerate device turn-off.

IBIC investigation of radiation-induced effects in CVD and natural diamond

A report is presented concerning the results obtained by Ion Beam-Induced Current (IBIC) investigations about the effects of radiation both on CVD and in natural diamond. Proton microbeam itself is used both to irradiate and to “probe” diamond samples particularly in their cross-sections as obtained by cleaving (“lateral IBIC”). Proton fluences and corresponding doses are limited normally to 10 8 p/cm 2 and to 2 Gy, respectively, leaving the possibility of an order of magnitude more. While in natural IIa diamond samples the charge collection efficiency is homogeneously distributed and it homogeneously increases as a function of proton dose, in CVD diamond samples it is not homogeneously distributed, it reflects the morphology of the samples and the main effect of irradiation is both to increase and to spread it over the low collection efficiency regions. Moreover, transient polarisation effects leading to lower collection efficiencies are reported both for CVD and diamond samples, in a way that seems to be dependent on the count rate registered by the “probe” beam.

Stress-induced defect migration in InP/InGaAsP double-heterostructure wafers

A low luminescence efficiency ring, concentric with the circular electrical contact, has been observed on p-InP and p-InGaAsP ( λ = 1.1 μm) epitaxial layers using cathodoluminescence imaging. This low efficiency region is found to be due to contact alloying. A mechanism based on the thermal migration of a defect in the strain field produced by the p-contact is proposed.

Photocurrent loss within the depletion region of polycrystalline solar cells

The collection efficiency of carriers optically generated within the depletion region of polycrystalline solar cells is analysed. The extent of the low collection efficiency region surrounding grain boundaries is shown to be very much smaller in the depletion layer than in the bulk quasi-neutral regions of the cells. For the optimum case where the grain boundaries are perpendicular to the edges of the depletion layer, it is shown that, near the centre of the layer, the low collection efficiency area extends only a fraction of an extrinsic Debye length from the grain boundary.