Gallium Nitride Photodetector Measurements of UV Emission from a Gaseous CH4/O2 Hybrid Rocket Igniter Plume

Abstract

Owing to its wide (3.4 eV) and direct-tunable band gap, gallium nitride (GaN) is an excellent material platform to make UV photodetectors. GaN is also stable in radiation-rich and high-temperature environments, which makes photodetectors fabricated using this material useful for in-situ flame detection and combustion monitoring. In this paper, we use a GaN photodetector to measure ultraviolet (UV) emissions from a hybrid rocket motor igniter plume. The GaN photodetector, built at the Stanford Nanofabrication Facility, has 5 µm wide regions of AlGaN/GaN two-dimensional electron gas (2DEG) electrodes spaced by intrinsic GaN channels. In most applications, the ideal photodetector would exhibit a high responsivity to maximize the signal, in addition to a low dark current to minimize quiescent power. A performance metric which simultaneously captures these two values is the normalized photocurrent-to-dark current ratio (NPDR), defined as the ratio of responsivity to dark current, with units of W -1 . The NPDR of our device is record-high with a value of 6 x 10 14 W -1 and the UV-to-visible rejection ratio is 4 x 10 6 . The high rejection ratio is essential as it eliminates cross-sensitivity of the detector to visible light. The spectral response can be modeled as a rectangular window with a peak responsivity of 7,800 AW -1 at 362 nm and a bandwidth of 16 nm. The photodetector shows operation at high temperatures (up to 250°C). The NPDR still remains above 10 9 W -1 at the higher temperatures, and the peak wavelength shifts from 362 nm to 375 nm at 250°C. The photodetector was placed at three radial distances (3", 5.5", and 7") from the base of the igniter plume and the oxidizer-to-fuel ratio (O2/CH4) was varied to alter the size and strength of the plume. The current measured from the device was proportional to the intensity of the emission from the plume. The data demonstrates a clear trend of increasing current with increasing fuel concentration. Further, the current decreases with larger separation between the photodetector and the plume. A calibration curve constructed from the responsivity measurements taken over four orders of magnitude was used to convert the current into incident optical power. By treating the plume as a black body, and calculating a radiative configuration factor corresponding to the geometry of the plume and the detector, we calculated average plume temperatures at each of the three oxidizer-to-fuel ratios. The estimated plume temperatures were between 850 and 950 K for all three combustion conditions. The temperature is roughly invariant for a fixed fuel concentration for the three tested distances. These data demonstrate the functionality of GaN as a material platform for use in harsh environment flame monitoring.

3C-SiC/Si heterostructure for self-powered multiband (UV-VIS) photodetection applications

“…Next, the performance of the two photodetector configurations were evaluated by their sensitivity, responsivity, and detectivity. Sensitivities were calculated as S=[(I on -I off )/I off ] × 100, which revealed 1.0×10 5 for the 3C-SiC/Si HET and 7.7×10 4 for the MSM under white light illumination (2.8 mW cm −2 ). Responsivity is a measure of electrical output gained from an incoming optical signal and it is calculated as R=(I on -I off )/(AxP light ), where A is the effective illumination area, and P is the light power intensity.…”

“…To meet the operational requirements of ever-growing industries such as power management, optical communications, automotive, aerospace, and defense, development of sensitive optical sensing devices gained a vast attention, where optical imaging, gas and ozone sensing, flame and combustion monitoring, and pollution control are essential [1][2][3][4][5][6]. In such applications, photodetectors (PD) are required to work at high temperatures and/or corrosive environments with high sensitivity in a wide spectrum light detection.…”

“…Photodetectors comprised of a single semiconductor material have the limitation of a narrow-band detection, in which only a small range of wavelengths can be detected with high sensitivity. To increase the absorption of the incident light and the spectral sensitivity of photodetectors, various heterostructures have been investigated such as CsPbBr3/ Si(100) [7], Al 2 O 3 /SiO 2 /4H-SiC [8], AlGaN/GaN-on-Si with Ti/Al/Pt/Au ohmic contacts [5], WSe 2 /polyimide (PI) [9], ZnO-CdS core-shell Micro/nanowire [10], Ga 2 O 3 /SiC [11], In 2 S 3 /glass [12], Cd 3 As 2 /MoS 2 [13], and Sb 2 Te 3 /n-Si [14]. Additionally, the research on self-powered devices has been intensified due to the increased demand for fabricating sustainable and eco-friendly electronic/photonic devices [15][16][17][18][19][20].…”