Si-Based ZnO Ultraviolet Photodiodes

Abstract

We are IntechOpen, the first native scientific publisher of Open Access books 12.2%108,000 1.7 M TOP 1% 151 3,350Chapter 6 Si-Based ZnO Ultraviolet Photodiodes Lung-Chien ChenAdditional information is available at the end of the chapter http://dx.doi.org/10.5772/48825 . IntroductionSemiconductor-based ultraviolet UV photodiodes have been continuously developed that can be widely used in various commercial, civilian areas, and military applications, such as optical communications, missile launchinμ detection, ame detection, UV radiation calibration and monitorinμ, chemical and bioloμical analysis, optical communications, and astronomical studies, etc. [ -]. All these applications require very sensitive devices with hiμh responsivity, λast response time, and μood siμnal-to-noise ratio is common desirable characteristics. Currently, liμht detection in the UV spectral ranμe still uses Si-based optical photodiodes. Due to the Si-based photodiodes are sensitive to visible and inλrared radiation, the responsivity in the UV reμion is still low [ -]. To avoid these disadvantaμes, wide-bandμap materials such as diamond, SiC, III-nitrides and wide-bandμap II-VI materials are under intensive studies to improve the responsivity and stability oλ UV photodiodes, because oλ their intrinsic visible-blindness [ ].Amonμ them, zinc oxide ZnO is another wide direct bandμap material due to its sensitive and UV photoresponse in the UV reμion [ -]. ZnO has attracted attention as a promisinμ material λor optical devices, owinμ to its larμe direct band μap enerμy oλ . eV and a larμe exciton bindinμ enerμy oλ meV at room temperature compared to other II-VI semiconductors [ -]. Thereλore, ZnO is promisinμ λor use in liμht-emittinμ diodes LEDs , laser diodes LDs , ultraviolet UV detection devices [ -]. Several deposition methods have been employed λor the μrowth oλ ZnO layers, includinμ metal-orμanic chemical vapor deposition MOCVD , molecular beam epitaxy MBE , pulsed laser deposition PLD , sol-μel and spray pyrolysis [ -]. The synthesis oλ p-type ZnO λilms with acceptable stability and reproduci-

Role of p-NiO electron blocking layers in fabrication of (P-N):ZnO/Al:ZnO UV photodiodes

“…This promotes the formation of depletion region across the p-n junctions and a potential difference is developed at the junction interface. Upon illumination of UV light with energy greater than the bandgap of the ZnO (E hν > E g ), the absorbed photons generate electron-hole (e-h) pairs in the depletion region [38]. When the diode is applied with reverse bias, the carriers are swept apart due to a built-in electric field.…”

“…Also due to barrier height of NiO, it helps to block the photogenerated carriers to flow back and hence M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 12 prevents the recombination of e-h pairs [14]. The photoresponsivity (R) of the fabricated photodiodes is defined as the ratio of photocurrent to that of input power of the UV light source and calculated using the following relation [15,38,40] x 10 2 % and 1.87 x 10 3 % respectively. The detectivity (D) of the fabricated photodiodes is calculated using the following relation [15,40] M A N U S C R I P T…”

High-speed photoresponse properties of ultraviolet (UV) photodiodes using vertically aligned Al:ZnO nanowires

“…Thus, a depletion region is formed at the interface of p–n junctions and a potential difference is developed. When the AZO15 nanowire UV photodiode is irradiated with UV light (365 nm), the valence electrons get excited and results in the formation of e‐h pairs in the depletion region . Under the reverse biased condition, the photogenerated electrons were drifted toward the conduction band (CB) of n‐AZO15 nanowires and the photogenerated holes were drifted toward the valence band (VB) of p‐PNZO thin film layers.…”

“…By the relation mentioned above, the energy barrier for electrons (Δ E c ) was calculated as 2.95 eV and the energy barrier for holes (Δ E v ) was calculated as 2.52 eV. The photoresponsivity ( R ) of the fabricated photodiode is defined as ratio of photocurrent to the power of input UV light and calculated using the following relation , where the value of J UV is 81.65 mA cm −2 , J dark is 21.37 mA cm −2 , and P inc is the power of incident UV light which was 4 mW cm −2 . The calculated photoresponsivity ( R ) of the fabricated AZO15 nanowire UV photodiodes is 15.07 A W −1 .…”

“…The external quantum efficiency (EQE) of the fabricated photodiodes is the probability of the single incident photon illuminated on the photodiodes to generate the e‐h pairs, which contribute the photocurrent. The EQE of AZO15 nanowire UV photodiodes was calculated using the following relation , where R is calculated photoresponsivity ( R = 15.07 A W −1 ), λ incident is the wavelength of the incident UV light source (365 nm), h is Planck's constant, and c is the velocity of light. Using known values, the external quantum efficiency (EQE) of the fabricated photodiodes is calculated as 5.12 × 10 3 %.…”