2.1. Synthesis of CdTe Films and Microdots

Figure 1 shows the schematic experimental setup involved in the deposition of arrayed CdTe microdots on Bi coated indium tin oxide (ITO)/glass.CdTe films and microdots were selectively grown on Bi coated ITO/glass substrates by vapor phase epitaxy (VPE) method in a temperature controlled three-zone furnace. Bi films were first predeposited on precleanedITO/glass substrate via e-beam evaporator system as the specific substrate for selective growth of CdTe (20 nm). For this a grain type Bi metal source of 99.999% purity (Alfa Aesar product, Haverhill, MA, USA) was used. The film was deposited by using a shadow metal mask at a deposition rate of 1 Å/s at 2 × 10 ⁻⁶ Torr. The prepared substrate and CdTe bulk source (3.8 g, 99.888% purity Alfa Aesar product, Haverhill, MA, USA) was placed in Zone 2 (growth zone) and Zone 3 (source zone) of the VPE. The source to substrate distance was varied from 5 to 15 cm in order to obtain a clear micro dot pattern. The quartz chamber was pumped to a pressure of 2.4 × 10⁻³ Torr via rotary pump and unreacted (Ar) carrier gas was flown out at 60 sccm for 10 min before growth. The flow was maintained until the temperature had completely lowered after the growth. The temperatures of Zone 1 and Zone 2 were kept the same (250, 350 and 450 °C), while the temperature of Zone 3 was held at 600 °C. The temperature rise rate of all the samples was 10 degrees per minute and the growth time was 1 h. Bi was additionally coated on Al₂O₃ (111) and Si (100) substrates under similar growth conditions to determine their role as catalyst that effectively promotes the selectively growth of CdTe.

Apparatus for the deposition of the CdTe microdots arrays on Bi coated indium tin oxide (ITO)/glass.