Fabrication of n-ZnO/p-Si (100) and n-ZnO:Al/p-Si (100) Heterostructures and Study of Current–Voltage, Capacitance– Voltage and Room-Temperature Photoluminescence M.A.H. SHAH, 1,4 M.K.R. KHAN, 2,5 A.M.M. TANVEER KARIM, 1,6 M. M. RAHMAN, 2,7 and M. KAMRUZZAMAN 3,8 1.—Department of Physics, Rajshahi University of Engineering and Technology, Rajshahi 6204, Bangladesh. 2.—Department of Physics, University of Rajshahi, Rajshahi 6205, Bangladesh. 3.—Department of Physics, Begum Rokeya University, Rangpur 5400, Bangladesh. 4.—e-mail: hadiphys@gmail.com. 5.—e-mail: fkrkhan@yahoo.co.uk. 6.—e-mail: tanveer@ruet.ac.bd. 7.—e-mail: mozibur2000@yahoo.com. 8.—e-mail: mkzaman_phybuet@yahoo.com Heterojunction diodes of n-ZnO/p-Si (100) and n-ZnO:Al/p-Si (100) were fabri- cated by spray pyrolysis technique. X-ray diffraction (XRD), energy dispersive x- ray spectroscopy (EDX), and field emission scanning electron microscopy (FES- EM) were used to characterize the as-prepared samples. The XRD pattern indicates the hexagonal wurzite structure of zinc oxide (ZnO) and Al-doped ZnO (AZO) thin films grown on Si (100) substrate. The compositional analysis by EDX indicates the presence of Al in the AZO structure. The FESEM image indicates the smooth and compact surface of the heterostructures. The current–voltage characteristics of the heterojunction confirm the rectifying diode behavior at different temperatures and illumination intensities. For low forward bias voltage, the ideality factors were determined to be 1.24 and 1.38 for un-doped and Al- doped heterostructures at room temperature (RT), respectively, which indicates the good diode characteristics. The capacitance–voltage response of the hetero- junctions was studied for different oscillation frequencies. From the 1/C 2 –V plot, the junction built-in potentials were found 0.30 V and 0.40 V for un-doped and Al-doped junctions at RT, respectively. The differences in built-in potential for different heterojunctions indicate the different interface state densities of the junctions. From the RT photoluminescence (PL) spectrum of the n-ZnO/p-Si (100) heterostructure, an intense main peak at near band edge (NBE) 378 nm (3.28 eV) and weak deep-level emissions (DLE) centered at 436 nm (2.84 eV) and 412 nm (3.00 eV) were observed. The NBE emission is attributed to the radiative recombination of the free and bound excitons and the DLE results from the radiative recombination through deep level defects. Key words: Heterostructure, photoluminescence, ideality factor, built-in potential INTRODUCTION Many researchers have tried to fabricate zinc oxide- (ZnO) and Si-based heterostructures and have studied their surface and interface properties giving special attention to the optoelectronic prop- erties for utilization as an optoelectronic device. Since both p-type and n-type Si and often p-ZnO are achievable, it is therefore possible to fabricate different types of heterostructures, for example, n- ZnO/p-Si, p-ZnO/p-Si, n-ZnO/n-Si, p-ZnO/n-Si, etc. Among these, p-ZnO/p-Si and p-ZnO/n-Si are diffi- cult to fabricate, because ZnO is naturally an n-type semiconductor. Many attempts have been made in (Received May 29, 2017; accepted October 10, 2017; published online October 25, 2017) Journal of ELECTRONIC MATERIALS, Vol. 47, No. 1, 2018 DOI: 10.1007/s11664-017-5873-2 Ó 2017 The Minerals, Metals & Materials Society 879