Surface Modification of AlN Using Organic Molecular Layer for Improved Deep UV Photodetector Performance

Abstract

A direct wide bandgap of 6.2 eV, high temperature robustness, and radiation hardness make aluminum nitride (AlN) a preferable semiconductor for deep ultraviolet (UV) photodetection. However, the performance and reliability of AlN-based devices is adversely affected by a large density of surface states present in AlN. In this work, we have investigated the potential of a monolayer of organic molecules in passivating the surface states of AlN, which improved the performance of AlN-based metal− semiconductor−metal (MSM) deep UV photodetector. The organic molecules of the meso-5,10,15-triphenyl-20-(p-hydroxyphenyl)porphyrin Zn(II) complex (ZnTPP(OH)) were successfully adsorbed on an AlN surface, forming a self-assembled monolayer (SAM). The molecular layer was characterized by contact angle measurement, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The surface modification of AlN effectively reduced the dark current of the photodetector by 10 times without degrading the magnitude of photocurrent, especially at low voltages. The photo to dark current ratio (PDCR) was enhanced from 930 to 7835 at −2 V, and the responsivity doubled from 0.3 to 0.6 mA/W at 5 V. Moreover, the rise and fall times of the detector were found to decrease after the surface modification process. Our results suggest that SAM of porphyrin molecules effectively passivated the surface states in AlN, which resulted in improved photodetector performance.

Organic passivation of Al0.5Ga0.5N epilayers using self-assembled monolayer of Zn(II) porphyrin for improved solar-blind photodetector performance

“…The wafer was diced into small samples of size 5 mm × 5 mm, which were cleaned in de-ionized (DI) water, acetone, and isopropyl alcohol (IPA) using the standard procedure. 27 For the passivation, the surface of bare Al0.5Ga0.5N was activated by immersing in H2SO4: H2O2 (3:1) solution for 20 minutes. 30 The samples obtained thereafter were referred to as the hydroxylated samples.…”

“…The hydroxylated samples were rinsed with DI water and dipped into ZnTPP(OH) solution (prepared by dissolving 1 mg ZnTPP(OH) compound in 5 ml Toluene) for an optimized time of 2 hours. 27 After this, the samples were rinsed with IPA, dried using dry nitrogen, and connected to the EverBeing DC probe station (EB-6). For photodetection measurements, an assembly of Xenon lamp (75 W), monochromator (Bentham TMC 300), optical fiber (PCU-1000), power meter and sensor (Thor Laboratories) was used.…”

“…As shown in FIG. 6 (d Besides improving the PDCR, SAM also led to an improvement in the responsivity of the photodetector, which is expressed as 27,44,45 :…”

“…The end group remains away from the Al0.5Ga0.5N surface, and backbone links the head group to the end group. [25][26][27][28][29] The reported method of wet passivation opens up the route to easily reproducible, less error-prone and cost-effective passivation schemes for…”

2D Layered Materials for Ultraviolet Photodetection: A Review

“…Traditionally, UV photodetection is achieved using bulk wide bandgap semiconductors such as GaN, Al x Ga 1− x N, AlN, Ga 2 O 3 , SiC, and diamond. [ 20–22,40 ] However, these materials fail to meet the demand of the upcoming market of new‐generation miniaturized, bendable, and wearable photodetectors. The challenges posed by bulk wide bandgap semiconductors can be overcome by using appropriate 2DLMs for this purpose.…”