The Influence of Substrate Temperature on the Near-infrared Absorption and Carrier Mobility of Lead Phthalocyanine Phototransistors

Abstract To improve their near-infrared photosensitive properties, lead phthalocyanine (PbPc) phototransistors were fabricated at different substrate temperatures (Ts) of 60, 100, 140 and 180°C in this paper. The crystal structure, absorption spectra and surface topography of PbPc films were tested. And the photosensitive properties of the devices were measured, the results showed that the photoresponsivity (R), maximum photo/dark current ratio (Pmax) and specific detectivity (D*) of the devices first increase and then decrease with Ts increasing and the optimum performances for R, Pmax and D* are acquired at Ts = 100°C. The relations among substrate temperature, film properties and device performance were studied, which indicated that the phase structure, crystallinity, interconnection of grains, carrier mobility and near-infrared absorption of the PbPc films can be altered via substrate heating, and thus giving rise to the changes in device performance. In addition, a mathematic model that semi-quantitatively describes the relationships of photocurrent versus photoabsorption coefficient and carrier mobility was established.