Etching photoanodic

While the cell efficiencies of these films were not specifically investigated, best parameters of 2 mAcm (ca. AMI illumination quantum efficiencies increased with decreasing illumination intensity due to diffusion limitations in the nanoporous film) 0.5 V and ca. 50% fill factor were obtained. However, great variation in these parameters were obtained one reason for this can be seen from a consideration of Figure 9.9. If a CdSe film is etched, but less than optimally (shorter time, more dilute HCl), it is clear that after a certain, unique etch treatment, zero net photocurrent will be obtained. The actual photocurrent (and other ontpnt parameters) of the film is a balance between photoanodic and photoca-thodic cnrrents. 

Out of the above three methods of light-sensitive etching, the one with polarization from an external source [case (a)], called photoanodic etching, and etching in oxidizing solution [case (c)], called photochemical etching, are now of the greatest practical importance. 

Fig. 21. Schematic diagram of an electrochemical cell for laser photoanodic etching. RE denotes electrolytic bridge to the reference electrode.

Fig. 22. Holographic photoanodic etching of CdS the diffraction reflex intensity Jiln, (curve 1), the ratio of the coefficients of mirror reflection from the etched (R) and original, nonetched (R0) surface (curve 2), and the depth of the sinusoidal relief 2h (curve 3) versus the ratio of the passed amount of electricity Q to an optimal amount (0 , ). [From Tyagai et at. (1978).]...

As in the case of photoanodic etching, a certain optimal time exists here, during which the etched relief attains the most regular shape a maximum value of diffraction efficiency corresponds to this time. 

Comparison of both the methods—photoanodic and photochemical etching—shows (see Table I) that they give approximately the same results, as far as resolution is concerned. Photochemical etching is a more universal method because it is equally applicable to the treatment of both n- and p-type... 

Figure 6. Effect of chemisorption of Ru3 on the grain boundaries of a chemically vapor-deposited, thin-film n-GaAs photoanode. The grains are of 3-5 pm in size. The current-voltage characteristics shown are for the n-GaAs/0.8M KnSe-0.1 M KsSet-lM KOH/C cell. ((-------------) freshly etched (---) Ru3 chemisorbed)...

HF or H2O. A wide range of processes, including pore formation in n- and p-type silicon in HF solutions, pore formation in n-type silicon in HF solutions under illumination, and photoanodic dissolution of n-type silicon in NH4F solutions, can be explained by these models. In addition, they are consistent with the models developed for open-circuit etching of silicon in fluoride solutions, discussed in Sec. 2.2.2. 

When etching n-GaP photoanodically in the onset region I of the photocurrent-potential curve (Table 2, cases M, N, O), etch hillocks and ridges are observed at the surface after removal of only a small amount of material (see, e.g., Fig. 20). In this region of the i- V curve, recombination of the photogenerated charge carriers... 

Photoetched (111)- and (TTT)-faces of GaP in alkaline OBr solutions show a remarkable difference in terms of morphology etch hillocks develop on n-GaP (similar to those formed by photoanodic etching of n-GaP in the onset region of the photocurrent-potential curve), whereas etch pits are formed on p-GaP (similar to those formed by anodic etching of p-GaP in the rising part of the i- V curve) [31]. 

Tenne R. and Hodes G. (1980), Improved efficiency of cadmium selenide photoanodes by photoelectrochemical etching , Appl. Phys. Lett. 37, 428-430. Tomkiewicz M., Ling 1., and Parsons W. S. (1982), Morphology, properties, and performance of electrodeposited normal CdSe in liquid-junction solar cells ,... 

Light-sensitive etching with polarization from an external source is called photoanodic etching, and that in an oxidizing solution, photochemical etching. 

Several methods of anodic (photoanodic in particular) etching have been suggested in the literature to reveal various inhomogeneities in the structure and composition of semiconducting crystals (see, e.g.. Refs. 104-106). 

Compound Semiconductors, Electrochemical Decomposition, Fig. 5 Single crystal SiC MEMs structure fabricated by photoanodic etching of n-SiC (Ref [22]. Reprinted with permission from Elsevier 2011)... 

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