Growth of CdSe and CdTe crystals shaped by thick alumina membranes

CdSe and CdTe semiconductors were deposited on single-crystal substrates by means of the simple isothermal closed space sublimation (ICSS) method using thick commercial alumina membranes as masks. By placing 60-nm-thick alumina membranes between the substrates and the incoming vapors, CdSe and CdTe small crystals were grown coherently on the surface of GaAs following the pattern of the membranes, whereas CdSe crystals with random crystalline orientations grew over Si substrates. Simultaneously, CdSe crystals grew inside the 200 nm diameter pores, along their complete length, from one surface of the membrane to the other. The growth of CdTe inside the pores was not efficient, and only few isolated crystals were observed. Electron microscope images and X-ray diffraction patterns allowed determination of the morphology and the structure of the grown material. Optical reflectance was used to verify the characteristics of CdSe thin films used as a reference.