Etching of III-V Compound Semiconductors

As stated in the introduction, wet etching processes may proceed either with or without external current flow. In the former case, the semiconductor crystal is incorporated as an electrode in an electrochemical cell and polarized anodically under illumination or in darkness for n- and p-type samples, respectively, leading to dissolution of the sample (see Sec. 2). This is referred to as the (photo)anodic etching process. 

In the case of open-circuit etching processes, no electrical contacts are required at the back of the sample, which is more attractive from a technological point of view the semiconductor crystal is simply immersed in the etchant solution and in some cases illuminated with light of an appropriate wavelength. Depending on the mechanism, three types of open-circuit etching processes can be distinguished, i. e., 

It was probably Gerischer who, as early as in the 1960s, first recognized the value of semiconductor electrochemistry for investigating the mechanisms of these open-circuit etching processes [27, 38, 68-70]. 

In the case of photoetching, the mechanism is again electrochemical, with two partial currents cancelling each other electrically but not chemically [5, 71]. Under illumination, electron-hole pairs are created the conduction band electrons reduce a dissolved oxidizing agent, whereas the holes oxidize the semiconductor. This model implies that at rest potential K, the photoetch rate (i.e., the etch rate under illumination minus the etch rate in the dark, both at a potential corresponding to under illumination) should correlate with the net photocurrent density at Vr under 

In the next part (Sec. 3.3), the morphology of the etched surfaces is discussed. It is shown that a strategy of combining kinetic, morphological, and electrochemical 

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