A Highly Sensitive and Robust GaN Ultraviolet Photodetector Fabricated on 150-mm Si (111) Wafer

New Charge Carrier Transport‐Assisting Paths in Ultra‐Long GaN Microwire UV Photodetector

“…Thus, the narrow channel width (10 µm) is necessary for the trap‐assisted PF mechanism to transport charge carriers when a low bias voltage (less than negative or positive 5 V) is applied. [ 51 ] Both defect‐free NWs and ultra‐long MWs samples had identical device structures and fabrication process parameters such as channel width and electrode thickness. The photoconductive performance of PDs is determined by photocurrent ( I Ph ) and photo‐to‐dark current ratio (PDCR), photoresponsivity ( R ), external quantum efficiency ( η ), and specific detectivity ( D * , unit: Jones = cm Hz 1/2 W −1 ), which can be expressed as [ 12,52 ] $$$$\begin{equation}{I}_{{\mathrm{Ph}}} = {I}_{\mathrm{L}}\ - {I}_{\mathrm{D}}\end{equation}$$$$ $$$$\begin{equation}{\rm{PDCR}}\; = {{{I}_{{\rm{Ph}}}} \over {{I}_{\rm{D}}}}\end{equation}$$$$ $$$$\begin{equation}R\ = \frac{{{I}_{{\mathrm{Ph}}}}}{{PA}}\ \end{equation}$$$$ $$$$\begin{equation}\eta \ = \frac{{hc}}{{e\lambda }}\ R\ \end{equation}$$$$ $$$$\begin{equation}{D}^* = \frac{{R{A}^{1/2}}}{{{{\left( {2e{I}_{\mathrm{D}}} \right)}}^{1/2}}}\end{equation}$$$$where I L , I D , P , A, h, c, e , and λ are light‐generated current, dark current, optical power density, active area of the channel (0.1 mm × 10 mm), Planck's constant, velocity of light, electron charge, and excited light wavelength (325 nm), respectively.…”

“…As for the MW structure‐based PD, the extracted photo‐response time ( τ Rise = 2.83 ms and τ Decay = 3.57 ms) is about 1.5 times shorter than that of the NW structure‐based PD despite of long transport path inside the MW structure. The response time is related to the separation and recombination of photo‐generated carriers, and due to the trap‐assisted transport paths by the PF effect, [ 50,51 ] the photo‐generated carriers can effectively be collected to the back‐to‐back electrodes through the paths under large electric fields.…”

“…[ 48,49 ] In‐depth analysis of dark current mechanisms is necessary in order to fully understand the photoconductive properties of realized n‐GaN 1D nano/microstructures, as well as mechanisms of charge carrier transport that are impacted by the trap‐assisted Poole–Frenkel (PF) effect, which is common in UV PDs based on GaN structures with trap level caused by internal crystal defect. [ 50,51 ] Figure a,d‐1 displays a typical schematic diagram of a device structure fabricated using n‐GaN MWs with an energy band diagram indicating the presence of trap levels at the interface between GaN and Si in the MSM junction, and also an optical micrograph (top view) for the photoconductive channel width corresponding to 10 µm of the device is observed from the right inserted image in Figure 5b. In general, the PF effect is a phenomenon that affects the transport of charge carriers within materials that contain crystal defects shown in Figure 3d under a large electric field.…”

“…In general, the PF effect is a phenomenon that affects the transport of charge carriers within materials that contain crystal defects shown in Figure 3d under a large electric field. [ 50,51 ] The PF effect is one of the models that explain charge carrier transport in an ionized state. Specifically, it describes the promotion of charge carrier transport by crystal defects present only under a large electric field (above approximately ±1 kV cm −2 ).…”

“…Thus, the narrow channel width (10 μm) is necessary for the trap-assisted PF mechanism to transport charge carriers when a low bias voltage (less than negative or positive 5 V) is applied. [51] Both defect-free NWs and ultra-long MWs samples had identical device structures and fabrication process parameters such as channel width and electrode thickness. The photoconductive performance of PDs is determined by photocurrent (I Ph ) and photo-to-dark current ratio (PDCR), photoresponsivity (R), external quantum efficiency (𝜂), and specific detectivity (D * , unit: Jones = cm Hz 1/2 W −1 ), which can be expressed as [12,52] I Ph = I L − I D…”