Damaged surface layer

The EBSD technique measures the top few monolayers of a sample to determine its crystal structure. However, most polishing techniques leave a damaged layer on the samples. Even 1 or 0.25 pm diamond polish is not sufficient. For EBSD work, a final polish with colloidal silica (grain size 0.05 pm) is often required to remove the damaged surface layers. 

The conclusion that the photocurrents are limited by recombination has been verified recently by Karl and Sommer (1971) who also determined the value of the bimolecular electron-hole recombination constant. The shapes of the transients observed in these experiments are similar to those which are characteristic of damaged surface layers (see p. 181). In a similar way many workers have observed non-linear field dependences of the collected charge. In their study of durene, Burshtein and Williams (1977) show that a consideration in terms of Onsager s (1938) theory of geminate surface recombination appears to be unsatisfactory the results are best explained in terms of efficient deep trapping and/or recombination in a narrow region near the illuminated surface. 

Fig. 104. Equivalent circuits for the analysis of photocurrent-decay transients. The circuit elements are C, photocapacitor Rseries, total series resistance of the spectroelectrochemical cell Rl, load resistor Rin, internal leakage resistor R0, C , resistor and capacitor of counterelectrode solution interface Rd, resistance due to damaged surface layer.

Fig. 106. Photopotential decay transients following a ns illumination pulse on n-CdSe in contact with selenide solution. The lower curves show the mechanically polished electrodes with a damaged surface layer and the upper curves the same after etching.

Very fast recombination process can be studied by photoluminescence transients [182,199]. In this experiment, very short laser pulses are used and ultra-fast recombination studied. For a mechanically polished but unetched sample of n-CdSe, luminescence decay times of 50 ps were found due to recombination in the damaged surface layer. On etching, the quantum yield for luminescence and the decay lifetime were both substantially increased [182]. 

Further experimentation will be required to obtain more direct evidence of high dislocation densities and to show quantitative correlation with electrical and other properties. If such evidence cannot be found then another explanation must be sought to account for the properties of damaged surface layers on semiconductors. 

Electrolytic etching of semiconductors is used to remove damaged surface layers on single crystal material and/or shape... 

Sullivan and Eigler (42) developed a technique for removing the damaged surface layer from the p-n junction area of germanium diodes without masking. The germanium diode is placed inside a hairpin-shaped platinum cathode and a stream of 0.1% KOH is allowed to flow down between the cathode and the germanium. Surface tension confines the electrolyte to the junction area. A polished surface is usually completed in 1 to 2 min at 1. 5 amp/cm. ... 

The basic equations will be reviewed, and applied to laser annealing. Laser annealing is, among other things, a promising method of recrystallizing the damaged surface layers of a... 

Special features If production is interrupted, lower cylinder temperatures to 160-170 °C only, as cool PC adheres strongly to the cylinder wall. Cylinder, screws and nozzles must usually be thoroughly cleaned if the injection moulding compound is changed. Otherwise, dark particles may become detached from the heat-damaged surface layer upon re-starting and influence the component quality. 

Fig. 3.24. Schematic of the processes involved in mechanical polishing, (a) smoothed surface after lapping containing dents and flaws, (b) removal of the large unevenness, (c) filling of dents and flaws with removed silica gel (1), (d) removal of the interim layer, (e) removal of the damaged surface layer and (f) the polished surface...

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