Study Of Porous InP Arrays Formed By Electrochemical Etching

Electrochemical etching, which has the features of low temperature, low damage, simplicity and low costs in the etching process, can be used to prepared nano-materials. With this method, porous silicon had been prepared in the early 1990s. Motivated by the study of porous silicon, lots of researchers have been attracted by porous compound semiconductors due to their high carrier mobility and some specific optical properties. However, the etching process ofⅢ-Ⅴcompound materials is more complicated than that of Si, and the mechanism of the etching has not been understood yet.In this paper, we choose the InP as the material to study its electrochemical etching process for its priorities compared to GaAs. It has been found that porous structure is varied with etching conditions, indicating a possibility of regular pores array if the optimal condition could be used.We also found that most macropores layer of the etched samples usually covered by micropores layer with minute diameters, whose pore-size can be far more different from macropores layer's. Comparing the pores formation on scratched surface with intact surface of samples, we found macropores imaged prior to the former one, showing that the preprocessing is important to define the pores initial position. The reason is given in the paper. It is also found sometimes branchs appear in many samples, and the smooth degree of pore wall increases with the pores deepening,demonstrated the possibilities of pores arrays with smooth wall if optimal condition is offered. This is analyzed in the paper.Further more, the etching of samples with different doped concentrations are studied. It is found that pore's depth and diameter on n-InP with heavily doped concentration is larger than moderately doped samples.Finally, we discussed the current oscillation in etching process. At constant voltage condition, the periodical current oscillation is observed in the experiment, and only appears at the voltage larger than 1.3V. The amplitude increases with the imposed voltage. During the oscillation in large amplitude, there are many random small amplitude oscillations. Comparing the cross section SEM of pores with the I-t curve, large oscillation unexpectedly coincident with porous layer, we analyzed the large and small oscillation based on V. Lehmann and Jens models, respectively.