Inhibition of unintentional extra carriers by Mn valence change for high insulating devices

Abstract

For intrinsic oxide semiconductors, oxygen vacancies served as the electron donors have long been, and inevitably still are, attributed as the primary cause of conductivity, making oxide semiconductors seem hard to act as high insulating materials. Meanwhile, the presence of oxygen vacancies often leads to a persistent photoconductivity phenomenon which is not conducive to the practical use in the fast photoelectric response devices. Herein, we propose a possible way to reduce the influence of oxygen vacancies by introducing a valence change doping in the monoclinic β-Ga 2 O 3 epitaxial thin film. The unintentional extra electrons induced by oxygen vacancies can be strongly suppressed by the change valence of the doped Mn ions from +3 to +2. The resistance for the Mn-doped Ga 2 O 3 increases two orders of magnitude in compared with the pure Ga 2 O 3 . As a result, photodetector based on Mn-doped Ga 2 O 3 thin films takes on a lower dark current, a higher sensitivity, and a faster photoresponse time, exhibiting a promising candidate using in high performance solar-blind photodetector. The study presents that the intentional doping of Mn may provide a convenient and reliable method of obtaining high insulating thin film in oxide semiconductor for the application of specific device.The intrinsic semiconductors always exhibit unintentional n-or p-type conductivity induced by native defects such as vacancies or interstitials 1,2 , leading to a difficulty in achieving high insulating material and limiting their use in the specific devices such as photodetector, dielectric layer, etc. In particular, for oxide semiconductors, the conductivity is often seen to exhibit a pronounced dependence on partial pressure of oxygen during growth 3,4 . It seems logical, that this conductivity is related to the presence of oxygen vacancies which served as the electron donors leading to a decrease in resistivity, as has been assumed for many years. In fact, with recent advances in growth techniques, particularly perhaps the advent of novel schemes of molecular beam epitaxy, it has become possible to grow thin films of oxide materials, as required for device applications, with rather high structural quality [5][6][7] . Notwithstanding this, however, oxygen vacancies have long been 6-8 , commonly and inevitably still are, attributed as the primary cause of conductivity in oxide semiconductors. Meanwhile, the presence of oxygen vacancies in oxides often leads to a persistent photoconductivity phenomenon since the carriers trapped by oxygen vacancies have longer lifetime and drift back to their original states slowly 9,10 . It is not conducive to the practical use in the fast photoelectric response devices. Take ZnO based photodetector as an example, the response time would extend to the order of minutes or hours due to the presence of oxygen vacancies 9,10 . In this work, we propose a possible way to suppress the unintentional extra carriers which are induced by oxygen vacancies and reduce the influence of oxygen vacancies by introducing...

Ultrahigh Performance of Self-Powered β-Ga2O3 Thin Film Solar-Blind Photodetector Grown on Cost-Effective Si Substrate Using High-Temperature Seed Layer

“…The responsivity of 96.13 A W −1 was achieved under 5 V bias, which is reported to be the highest on a thin-film-based gallium oxide photodetector, demonstrating the good reliability to grow these photodetectors on an inexpensive Si substrate. 3,4,29,[35][36][37]44,45 Furthermore, the responsivity with the HSL-grown β-Ga 2 O 3 thin film photodetector has a rejection ratio more than 2 orders for 250 nm vs 400 nm, indicating its excellent solar-blind nature. Figure 4(b) shows the variation of the EQE with wavelength under various bias voltages, which is another important factor to determine the performance of a photodetector and is given by where R, h, c, e, and λ are the responsivity, Planck's constant, speed of light, electron charge, and wavelength of incident optical light, respectively.…”

“…In particular, for a thin-film-based planar photodetector a record-high responsivity and EQE are observed, which is even considerably higher than that of a solarblind β-Ga 2 O 3 photodetector fabricated on very expensive substrates. 4,24,29,[35][36][37]44,45,51 To determine the response rate and further explore the feasibility of the photodetector for practical applications as a solarblind photodetector, the real-time photocurrent transient response is studied by periodically switching a 254 nm optical signal on and off in self-power mode, without applying external power to the photodetector. For the β-Ga 2 O 3 thin film photodetector grown without HSL, the current increases to a non-stable value, and after switching off the optical signal the current does not reach its original value; rather, both the photocurrent and dark current consistently increase after repeated exposure, as shown in Figure 5(a).…”

“…Solar-blind photodetectors are an emerging technology for forest fires, territory intrusions, ozone hole monitoring, deep space exploration, satellites, and security communication. − A photodetector working in the <280 nm, solar-blind region could minimize the chances of false radiation detection even under intense sun interference on the earth’s surface by detecting ozone layer filtered deep UV (UV-C) terrestrial signatures. − Ideally, an efficient solar-blind photodetector must satisfy five “S” requirements, i.e., high sensitivity, high signal current-to-dark current ratio, high spectral selectivity, high speed, and high thermal stability. On top of all conventional five S requirements, a “self-powered” solar-blind photodetector has recently grabbed huge attention toward the goal to build an intelligent, wireless, exceptionally small, and sustainable photodetector …”

Ti- and Fe-related charge transition levels in β−Ga2O3

“…However, it is generally thought that significant p-type conductivity can not be achieved reliably in β-Ga 2 O 3 , due to i) no shallow acceptor dopants being available [77,78], ii) the likely formation of self-trapped holes [60,61] and iii) self-compensation [77]. There is, however, a number of deep acceptors, such as Fe [5,71,141], Mn [142], Mg [67,76,91,143], Al [76], Co [76], Ni [76] and N [143] which are used to produce semi-insulating β-Ga 2 O 3 needed, for example, as a base for β-Ga 2 O 3 -based power electronics (see Fig. 4.1).…”

Current advances in solar-blind photodetection technology: using Ga2O3 and AlGaN

“…This reduced PPC effect led to a fast recovery in the device from hours to <9 s upon turning off the incident light. 94 The PPC effect in Ga 2 O 3 PDs can be effectively suppressed by annealing in oxygen 110 or by doping divalent elements such as Zn and Mg. 111–114 Guo et al 115 reported that an SB photodetector based on β-Ga 2 O 3 exhibited a lower dark current and a faster response speed by Zn doping due to the reduction in the concentration of oxygen vacancies. Further, the band gap can be tuned continuously by alloying with different concentration ratios of Zn and Mg elements, which can remain unchanged with an appropriate ratio.…”