Heterojunction photodiode fabricated from hydrogen treated ZnO nanowires grown on p-silicon substrate

Abstract

A heterojunction photodiode was fabricated from ZnO nanowires (NWs) grown on a p-type Si (100) substrate using a hydrothermal method. Post growth hydrogen treatment was used to improve the conductivity of the ZnO NWs. The heterojunction photodiode showed diode characteristics with low reverse saturation current (5.58 Â 10 À7 A), relatively fast transient response, and high responsivity (22 A/W at 363 nm). Experiments show that the photoresponsivity of the photodiode is dependent on the polarity of the voltages. The photoresponsivity of the device was discussed in terms of the band diagrams of the heterojunction and the carrier diffusion process. Semiconductor nanowires (NWs) have garnered extensive research interests due to their unique optical and electrical properties. 1,2 In particular, ZnO NWs are promising for optoelectronic applications including ultraviolet (UV) lightemitting diodes (LED), UV laser diodes, and UV photodetectors for their wide band gap (3.37 eV), large exciton binding energy 60 meV, and high photoconductive gain. [3][4][5] The development of a ZnO pn junction has been limited by the difficulty of growing p-type ZnO. However, heterojunctions with ZnO NWs have been developed with p-type substrates including silicon. [6][7][8][9] The traditional bottom up approach is often employed which causes poor conductivity and high density of surface defects. Post growth hydrogen treatment is a simple and efficient method for the conductivity enhancement, which is intensively investigated both theoretically and experimentally. [10][11][12][13][14] The conductivity of ZnO could be enhanced by up to three orders of magnitude without significant changes in the structure and crystal orientation of the wurtzite type ZnO nanostructures. 12 The conductivity enhancement could be attributed to the introduction of shallow donor states such as the VO-H complex and the hydrogen interstitial. 15,16 Also, the passivation effect on the defects could reduce carrier scattering centers and hence has the potential to increase the electron mobility. 17 In this study, heterojunction photodiode was fabricated based on highly vertically aligned hydrogen treated ZnO NWs grown on top of p-Si substrate through hydrothermal method. A similar growth method has been reported by Ghosh and Basak for quasialigned ZnO NWs/p-Si heterojunction photodiode. 8 The heterojunction photodiode in this work shows a low reverse saturation current and relatively fast time response. The photoresponsivity spectra of the device in the UV and visible regions depend on the polarity of the applied voltages, which is explained in terms of energy band structure and carriers transportation mechanism inside the heterojunction structure.All chemical reagents were purchased from SigmaAldrich and used without further purification. Ammonium hydroxide (28 wt. %) was added dropwise into 0.1M zinc chloride solution until the pH is 10-11 and the solution was clear. Subsequently, the transparent solution was transferred to a Teflon-lined autoclave (Parr, USA) and th...

Ultraviolet Photodetection Properties of ZnO/Si Heterojunction Diodes Fabricated by ALD Technique Without Using a Buffer Layer

“…However, they [14] observed a very poor forwardto-reverse current ratio (~2 at ±4 V) with a very large reverse saturation current (~4.6×10 -5 A). After critical review of the above works, it is observed that, in general, the n-ZnO thin film grown on a suitable seed layercovered p-Si substrate can help to improve the performance of n-ZnO thin film/p-Si heterojunction photodetectors [9][10][11]. Since the growth of a seed layer is an additional step required in the fabrication process, the cost of fabrication is higher than that of the devices without seed layer.…”

“…As an alternative, many researchers are trying to explore the low-cost, environment friendly and wide band gap (~3.34 eV) zinc oxide (ZnO) material with large exciton energy (~60 meV larger than GaN ~25 meV) for the UV detection applications [5,6]. They have shown their interest to investigate ZnO based UV photodetectors with different configurations such as Schottky diode [5,6], MSM (metal-semiconductor-metal) [3,7,8], MISM (metalinsulator-semiconductor-metal) [2,8] and p-n heterojunction [9][10][11][12][13] photodiode structures. Since, ZnO is an intrinsically n-type semiconductor, the fabrication of a stable and controllable p-type ZnO thin film is very difficult [11].…”

“…Since, ZnO is an intrinsically n-type semiconductor, the fabrication of a stable and controllable p-type ZnO thin film is very difficult [11]. Hence, ZnO is employed as the n-type semiconductor layer in most of the ZnO based p-n heterojunction UV photodiode structures [10][11][12].…”

“…The ZnO thin films can be deposited on large Si wafer by various chemical and physical methods such as vapour transport [9], hydrothermal [10], thermal evaporation [11], pulsed laser deposition (PLD) [14], magnetron sputtering [15], atomic layer deposition (ALD) [16,17] and sol-gel techniques [12,13]. Luo et al [9] reported the fabrication of ZnO nanowire/Si heterojunction photodiodes via VLS (vapor liquid solid) growth mechanism with the help of gold as a catalyst.…”

Low-Temperature, Chemically Grown Titanium Oxide Thin Films with a High Hole Tunneling Rate for Si Solar Cells

“…Heterojunctions are widely used in optoelectronic devices such as light-emitting diodes (LEDs) [1][2][3][4], laser diodes [5,6], and photodiodes (PDs) [7][8][9] because they enable manipulating either hole or electron transport selectively by applying an appropriate band alignment. The specific band alignment can either increase carrier recombination in a LED or move photocarriers into appropriate contact in a PD.…”