Effect of Bias on the Response of GaN Axial p–n Junction Single-Nanowire Photodetectors

Abstract

We present a comprehensive study of the performance of GaN single-nanowire photodetectors containing an axial p-n junction. The electrical contact to the p region of the diode is made by including a p + /n + tunnel junction as cap structure, which allows the use of the same metal scheme to contact both ends of the nanowire. Single-nanowire devices present the rectifying current-voltage characteristic of a p-n diode, but their photovoltaic response to ultraviolet radiation scales sublinearly with the incident optical power. This behavior is attributed to the dominant role of surface states. Nevertheless, when the junction is reverse biased, the role of the surface becomes negligible in comparison to the drift of photogenerated carriers in the depletion region. Therefore, the responsivity increases by about three orders of magnitude and the photocurrent scales linearly with the excitation. These reverse-biased nanowires display decay times in the range of » 10 µs, limited by the resistance ´ capacitance time constant of the setup. Their ultraviolet/visible contrast of several orders of magnitude is suitable for applications requiring high spectral selectivity. When the junction is forward biased, the device behaves as a GaN photoconductor, with an increase of the responsivity at the price of a degradation of the time response. The presence of leakage current in some of the wires can be modeled as a shunt resistance which reacts to the radiation as a photoconductor and can dominate the response of the wire even under reverse bias.

Photodetecting properties of single CuO–ZnO core–shell nanowires with p–n radial heterojunction

“…The current–voltage characteristic of a single CuO–ZnO_2 core–shell nanowire contacted by EBL and FIBID (Fig. 6 f) exhibits a non-linear asymmetric shape indicating a rectifying behaviour emerging from the formation of a p–n radial heterojunction between the CuO core and the ZnO shell of the single CuO–ZnO core–shell nanowire, typical for a p–n diode 54 . The semilogarithmic representation for the single CuO–ZnO_2 core–shell nanowire (Figure S1 ) reveals a direct–reverse ratio of about 10 3 and the ideality factor of the p–n radial heterojunction diode based on this nanowire was estimated at about 1.5.…”

Constructing Caesium-Based Lead-Free Perovskite Photodetector Enabling Self-Powered Operation with Extended Spectral Response

“…51,52 Moreover, under an applied bias, weak thermal effects also improve the carrier generation and transport within the bulk perovskite material. 53 It is important to mention that R λ and D* commonly show a declining trend with an increase in incident light intensities. Typically, under higher incident light intensities, the number of photogenerated charge carriers that are available for extraction will be reduced.…”

“…In fact, under zero bias, the charge carrier transport is dominated through the diffusion process with a weak contribution from the drift current . However, at a higher voltage (1 V), the photoexcited carriers are driven by drift velocity, which ensures the effective charge transport and collection, leading to higher R λ and D * values. , Moreover, under an applied bias, weak thermal effects also improve the carrier generation and transport within the bulk perovskite material …”

Enhanced Photoresponse Performance of Self‐Powered PTAA/GaN Microwire Heterojunction Ultraviolet Photodetector Based on Piezo‐Phototronic Effect

“…What's more, it is resistant to high temperature, strong radiation, and has higher chemical stability, is widely used in harsh working environments. [15][16][17][18] Until now, different kinds of GaN-based self-powered PDs have been reported, [19][20][21][22][23] in which the organic/inorganic hybrid selfpowered PDs have gained tremendous research interest because of their unique properties combining the excellent intrinsic carrier mobility of inorganic materials and the abundant merits of organic components with tunable functionality, easy of fabrication, low cost and high flexibility. [24][25][26][27][28][29] Among various organic materials, PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl) amine]) is a typical π-electron conjugated polymer with a high hole transport rate (10 -3 up to 10 -2 cm 2 V -1 s -1 ), which has been widely applied in perovskite solar cells, polymeric light emitting diodes and organic field effect transistors owing to its good film-forming characteristic, nonwetting surface, transparency, and high stability, [30][31][32] thus may be a good choice in UV PDs.…”