As a potential candidate for inorganic FETs in various applications, organic FETs have received much attention during recent years. In order to remove surface contamination and to improve the device performance, surface treatment is generally adopted before deposition of organic films. However, the microstructure of the organic films is very sensitive to growth conditions. Surface treatment and heating can influence the film morphology and the device performance greatly. In order to study the effect of surface treatment on the growth of pentacene film, we deposited and contrasted pentacene films at room temperature and elevated temperature on SiO2 substrate treated by several typical cleaning procedures. The results indicated that surface treatment could influence the film morphology greatly even for a thickness far beyond the first monolayer. We also found that there was a low critical temperature of about 55 °C at a deposition rate of 0.5 nm/min, above which substantial desorption of pentacene molecule occurred regardless of the cleaning procedure. Deposition on heated substrates is widely reported for increased grain size and improved device performance, while the possible desorption seems to be seldom noticed. Therefore, an implication of the low desorption temperature is that the film thickness may be frequently overestimated for deposition on heated substrates. Consequently, errors for any data that are dependent on film thickness may be caused without taking into account the possible desorption.
- Organic molecular beam deposition
- Organic semiconductors