Fluorine Plasma Treatment for AlGaN/GaN HEMT-Based Ultraviolet Photodetector With High Responsivity and High Detectivity

Ultrahigh-Responsivity Ultraviolet Photodetectors Based on AlGaN/GaN Double-Channel High-Electron-Mobility Transistors

“…R is calculated by the formula of R = I photo − I dark A , I photo and I dark represent the photocurrent and dark current under the same bias condition, and A represent the area of gate region. The responsivity linearly increases as the light intensity decreases in double logarithmic coordinates, following a relationship of the form R ∝ P β–1 , where β is 0.35 and mainly related to the process including generation, recombination and trapping of the carriers. ,− For the as-fabricated AlGaN/GaN double-channel HEMT PD, the highest responsivity at 9.7 μW/cm 2 was remarkable as 2.1 × 10 7 A/W, which was much higher than that of previously reported GaN HEMT PDs, as shown in Table . This behavior was further evaluated by the term external quantum efficiency (EQE), which can be calculate by EQE = h c R λ q , where h , c , q , and λ are Planck’s constant, velocity of light, elementary electric charge, and light wavelength, respectively .…”

“…It can be calculated by the noise equivalent power (NEP): , D * = A × B NEP , where A is the active area, B is the electrical bandwidth. Generally, the NEP of the device can be estimated according to the equation: ,,, NEP = 2 q I D R , where q is the electronic charge constant and I D is the dark current density, and then the specific detectivity D * was calculated to be 4.36 × 10 16 Jones at 2 V. However, this specific detectivity value was overestimated because it only considered the short noise, but the noise of PDs commonly includes shot noise, thermal noise, and flicker (1/ f ) noise. , In order to more precisely measure specific detectivity, it is crucial to take into account the contribution of flicker noise at low frequency. Figure a shows the noise power spectra of PD measured in the frequency range of 1 to 100 kHz at various drain voltages.…”

“…It demonstrates that the device had a good transient response at a high frequency without peak-to-peak magnitude degradation. As compared with rise time, the apparently long fall time is mainly related to the persistent photoconductivity effect (PPC), which results from the capture and release of photogenerated carriers by deep-level defects, and has been widely reported in many GaN PDs. ,,− Further repairing etching damage and passivation treatments in the gate region are underway, and believed to largely shorten the response time and improve the device performance. − …”

“…Due to the strong polarization effects, high-concentration and high-mobility two-dimensional electron gases (2DEGs) often exist at the AlGaN/GaN heterojunction interface, which is quite beneficial to collect the photocurrent for high responsivity. − Recently, several studies of PDs based on AlGaN/GaN 2DEGs have been reported. − However, the 2DEG channel is naturally normally on even in the dark condition, which leads to high power consumption, low phototo-dark current ratio (PDCR) and poor detectivity. Several methods have been proposed to suppress the dark current for PDs, such as p-GaN gate, , semitransparent gate contact, p-oxide transparent gate, gate recessed .…”

Improving Performance of Al2O3/AlN/GaN MIS HEMTs via In Situ N2 Plasma Annealing

“…However, in order to reduce power loss during switching and to simplify circuit configuration, normally-off devices are necessary for power applications. Many technologies that could enable devices to achieve enhancement mode (E-mode) have been proposed, including fluorine ion treatment [ 8 , 9 ], p-GaN gate [ 10 ], thin AlGaN barrier [ 11 ], recessed gate [ 12 , 13 ], and so on. While the F ion implantation method appeared earlier, the F ion is easy to diffuse in the barrier layer at high temperatures, resulting in an unstable device threshold voltage.…”