Electrical, optical, and structural properties of indium-tin-oxide thin films for organic light-emitting devices

High-quality indium-tin-oxide (ITO) thin films (200-850 nm) have been grown by pulsed laser deposition (PLD) on glass substrates without a postdeposit ion annealing treatment. The structural, electrical, and optical properties of these films have been investigated as a function of target composition, substrate deposition temperature, background gas pressure, and film thickn ess. Films were deposited from various target compositions ranging from 0 t o 15 wt % of SnO2 content. The optimum target composition for high conducti vity was 5 wt % SnO2+95 wt % In2O3. Films were deposited at substrate tempe ratures ranging from room temperature to 300 degrees C in O-2 partial press ures ranging from 1 to 100 mTorr. Films were deposited using a KrF excimer laser (248 nm, 30 ns full width at half maximum) at a fluence of 2 J/cm(2). For a 150-nm-thick ITO film grown at room temperature in an oxygen pressur e of 10 mTorr, the resistivity was 4 x 10(-4) Omega cm and the average tran smission in the visible range (400-700 nm) was 85%. For a 170-nm-thick ITO film deposited at 300 degrees C in 10 mTorr of oxygen, the resistivity was 2 x 10(-4) Ohm cm and the average transmission in the visible range was 92% . The Hall mobility and carrier density for a 150-nm-thick film deposited a t 300 degrees C were 27 cm(2)/V s and 1.4 x 10(21) cm(-3), respectively. A reduction in the refractive index for ITO films can be achieved by raising the electron density in the films, which can be obtained by increasing the concentration of Sn dopants in the targets and/or increasing deposition tem perature. Atomic force microscopy measurements of these ITO films indicated that their root-mean-square surface roughness (similar to 5 Angstrom) was superior to that of commercially available sputter deposited ITO films (sim ilar to 40 Angstrom). The PLD ITO films were used to fabricate organic ligh t-emitting diodes. From these structures the electroluminescence was measur ed and an external quantum efficiency of 1.5% was calculated. (C) 1999 Amer ican Institute of Physics. [S0021-8979(99)04223-1].