Guodong Yuan

ZnO light-emitting diodes fabricated on Si substrates with homobuffer layers

ZnO homojunction light-emitting diodes (LEDs), comprised of N–Al codoped p-type ZnO and Al-doped n-type ZnO layers, were fabricated on Si substrates with homobuffer layers. The current-voltage measurements showed typical diode characteristic with a threshold voltage of about 3.3V. The electroluminescence (EL) bands at 110K consisted of a near-band-edge emission at 3.18eV and a deep level emission at 2.58eV. The EL emissions were assigned as radiative recombinations, presumably of donor-acceptor pairs, in the p-type layer of the LED. The quenching of EL with temperature was attributed to the degradation of p-type conducting of the ZnO:(N,Al) layer.

Electrical characterization of ZnO-based homojunctions

Electrical characteristics have been studied for ZnO p-n and p-i-n homojunctions, with optimization of device structures for improved performance. Capacitance-voltage measurements confirm the formation of abrupt junctions. The current-voltage characteristics exhibit their inherent electrical rectification behavior. The p-ZnO:(N,Al)∕n-ZnO:Al homojunctions fabricated on sapphire substrates combining with the intrinsic ZnO buffer layer have acceptable p-n diode characteristics, with the forward turn-on voltage of 1.4V and the reverse breakdown voltage of 5.3V. By introduction of an intrinsic (Zn,Cd)O layer, the resultant p-ZnO:(N,Al)∕i-(Zn,Cd)O∕n-ZnO:Al homojunction exhibits a high reverse breakdown voltage of ∼18V.

Convertibility of conduction type in Al-N codoped ZnO thin films based on DC reactive magnetron sputtering

p-type conduction in ZnO thin films was realized by an Al-N codoping method. ZnO thin films were prepared in an NH/sub 3/-O/sub 2/ atmosphere with the substrate temperature in the range of 360-540/spl deg/C with a 20/spl deg/C space. Secondary ion mass spectroscopy (SIMS) tests proved that the presence of Al facilitated the incorporation of N into ZnO. A conversion from n-type conduction to p-type in a range of temperatures has been identified by measurements of the Hall effect and spreading resistance profiles. The Nls peak is located around 405.6eV in Al-N codoped ZnO thin films, compared with 401.7eV in the N alone-doped case, which may be due to the formation of Al-N bonds. The obtained p-type ZnO films shows a resistivity of 24.5 /spl Omega/cm, hole concentration of 7.48/spl times/10/sup 17/ cm/sup -3/ at room temperature. A model showing nitrogen incorporation suggests the possibility of realizing p-type ZnO films of low resistivity by optimizing thermal annealing.