Impact of surface morphology of Si substrate on performance of Si/ZnO heterojunction devices grown by atomic layer deposition technique

Abstract

Articles you may be interested inImpact of annealing on the chemical structure and morphology of the thin-film CdTe/ZnO interface J. Appl. Phys. 116, 024312 (2014); 10.1063/1.4890235 CdS nanofilms: Effect of film thickness on morphology and optical band gap Growth morphology and electrical/optical properties of Al-doped ZnO thin films grown by atomic layer deposition J. Vac. Sci. Technol. A 30, 021202 (2012); 10.1116/1.3687939Texture vs morphology in ZnO nano-rods: On the x-ray diffraction characterization of electrochemically grown samplesIn this paper, the authors have investigated the structural, optical, and electrical characteristics of silicon nanowire (SiNW)/zinc oxide (ZnO) core-shell nanostructure heterojunctions and compared their characteristics with Si/ZnO planar heterojunctions to investigate the effect of surface morphology of Si substrate in the characteristics of Si/ZnO heterojunction devices. In this work, ZnO thin film was conformally deposited on both p-type h100i planar Si substrate and substrate with vertically aligned SiNW arrays by atomic layer deposition (ALD) method. The x-ray diffraction spectra show that the crystalline structures of Si/ZnO heterojunctions are having (101) preferred orientation, whereas vertically oriented SiNW/ZnO core-shell heterojunctions are having (002)-oriented wurtzite crystalline structures. The photoluminescence (PL) spectra of Si/ZnO heterojunctions show a very sharp single peak at 377 nm, corresponding to the bandgap of ZnO material with no other defect peaks in visible region; hence, these devices can have applications only in UV region. On the other hand, SiNW/ZnO heterojunctions are having band-edge peak at 378 nm along with a broad emission band, spreading almost throughout the entire visible region with a peak around 550 nm. Therefore, ALD-grown SiNW/ZnO heterojunctions can emit green and red light simultaneously. Reflectivity measurement of the heterojunctions further confirms the enhancement of visible region peak in the PL spectra of SiNW/ZnO heterojunctions, as the surface of the SiNW/ ZnO heterojunctions exhibits extremely low reflectance (<3%) in the visible wavelength region compared to Si/ZnO heterojunctions (>20%). The current-voltage characteristics of both Si/ZnO and SiNW/ZnO heterojunctions are measured with large area ohmic contacts on top and bottom of the structure to compare the electrical characteristics of the devices. Due to large surface to-volume ratio of SiNW/ZnO core-shell heterojunction devices, the output current rating is about 130 times larger compared to their planar version at 2 V forward bias voltage. This higher output current rating can be exploited for fabricating high-performance nanoelectronic and optoelectronic devices in near future.

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“…The lattice mismatch is not always considered essential to influence on the growth mechanism and film quality, while the synthesizing method has curtail effect on film crystalline quality 20,21 and its behaviors, this phenomena has been observed and studied very well in previous works using several deposition techniques 8,12 . For very thin films the properties will be dominated by the several materials used in interface favorite the nanostructural nucleation and play a catalyst role 7 , which has been observed recently 22 . On the other hand, the optical, sensing and electrical 7 properties have been sensible to the doped dose as well as metal nature like Cu, Zn, Pb or Ag 5 .…”

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