Mg thermal diffusion behavior on the band modulation of MgxZn1-xO/ZnO metal-semiconductor-metal photodetectors

By magnesium (Mg) atom diffusion in ZnO layer, the detection band of MgxZn1-xO/ZnO metal-semiconductor-metal photodetectors (MSM-PDs) could be modulated from two distinct bands to one band. ZnO and MgxZn1-xO layers were deposited consecutively on a sapphire substrate using an radio-frequency magnetron sputtering system. With increasing annealed temperature, Mg atoms diffuse from MgxZn1-xO into the underlying ZnO layer, which tunes the composition of ZnO into MgyZn1-yO and thus modulate the detection band of MSM-PDs. For the annealed temperature below 900 °C, two distinct bands were detected in the MSM-PDs with wavelength region of 280-330 nm and 360-400 nm due to the absorption of MgxZn1-xO and underlying ZnO layers. Further increasing the annealed temperature to 900 °C, the deeply diffusing Mg atom causes the MgxZn1-xO and ZnO layers were homogenized into a uniform MgzZn1-zO layer, hence the detection band was transformed into one band with a wavelength region of 280-340 nm. Secondary ion mass spectrometry depth profile showed the Mg atom diffusing downwards with increasing annealed temperature, causing the Mg content to decrease from ~ 30% in the as deposited MgxZn1-xO to ~ 8% in the homogenized MgzZn1-zO layer. Photoluminescence demonstrated the as-deposited MgxZn1-xO/ZnO bi-layer having two distinct emission peaks around 340 and 400 nm, and the MgxZn1-xO and ZnO layers were homogenized into a MgzZn1-zO layer in 900 °C and hence only one emission peak (355 nm).