Aluminum doped zinc oxide (AZO) thin film is gaining momentum as a transparent conducting oxide because its optical and electrical properties are optimal for a photovoltaic device. We report growth of AZO thin film using an Atomic Layer Deposition (ALD) system, which is known to deposit layers on a substrate with atomic layer precision. The precursors used for aluminum and zinc were Trimethylaluminum (TMA) and Dimethylzinc (DMZ) respectively. Alternating cycles of TMA and DMZ were introduced to the heated deposition chamber such that a desired aluminum doping was obtained on the AZO films grown. The films were grown on flexible substrates like PET and also on single crystalline Si(100) and float-glass substrates. An optimal aluminum doping (3 at.%) on the AZO film of thickness 575 nm gave a sheet resistance (Rs) of 97 Ω/□ with corresponding resistivity of 5.6 x 10-3 Ω.cm. The value of the carrier concentration and hall mobility were 1.86 x 1020 cm-3 and 6.5 cm2V-1s-1 respectively. Optical measurement showed 90% transmission in most of the visible spectrum. X-ray diffraction spectra of the film showed all characteristic ZnO hexagonal lattice peaks.