Comprehensive characterization of metal–semiconductor–metal ultraviolet photodetectors fabricated on single-crystal GaN

Abstract

We report on the material, electrical, and optical properties of metal–semiconductor–metal ultraviolet photodetectors fabricated on single-crystal GaN, with active layers of 1.5 and 4.0 μm thickness. We have modeled current transport in the 1.5 μm devices using thermionic field emission theory, and in the 4.0 μm devices using thermionic emission theory. We have obtained a good fit to the experimental data. Upon repeated field stressing of the 1.5 μm devices, there is a degradation in the current–voltage (I–V) characteristics that is trap related. We hypothesize that traps in the GaN are related to a combination of surface defects (possibly threading dislocations), and deep-level bulk states that are within a tunneling distance of the interface. A simple qualitative model is presented based on experimental results. For devices fabricated on wafers with very low background free electron concentrations, there is a characteristic “punch-through” voltage, which we attribute to the interaction of the depletion region with the underlying low-temperature buffer layer. We also report GaN metal–semiconductor–metal photodetectors with high quantum efficiencies (∼50%) in the absence of internal gain. These photodetectors have a flat responsivity above the band gap (measured at ∼0.15 A/W) with a sharp, visible-blind cutoff at the band edge. There is no discernible responsivity for photons below the band-gap energy. We also obtained record low dark current of ∼800 fA at −10 V reverse bias. The dark current and ultraviolet photoresponse I–V curves are very flat out to VR>−25 V, and do not show evidence of trap-related degradation, or punch-through effects.

The heterogenous integration of GaN thin-film metal-semiconductor-metal photodetectors onto silicon

“…This degradation is within the error tolerance of the measurements. The 10-V low bias dark current of 1.01 pA of the thin-film GaN MSM detector is comparable to the best reported low bias dark current of 0.8 pA at 10 V for onwafer MSMs with similar area and finger spacing, but with a 4 m thick GaN layer [9]. The best reported 1-m-thick GaN onwafer MSM had a dark current of approximately 50 pA at 10 V [9].…”

High-sensitivity β-Ga_2O_3 solar-blind photodetector on high-temperature pretreated c-plane sapphire substrate

“…In general, there is an internal gain (G) mechanism in MSM PDs due to the trapping of minority carriers at/near the metal/β-Ga 2 O 3 interface (see process 1, Fig. 5), which often dominates the scale of responsivity [24]. G can be estimated by…”

Photoconductors for Measuring Speckle Motion to Monitor Ultrasonic Vibrations

“…This occurs through several mechanisms, including image force lowering (the Schottky effect), (Neamen, 2003;Soares, 1992) charge tunneling from the metal across the barrier (Soares, 1992), and photogenerated charge accumulation (Soares, 1992;Carrano, 1998). By these processes, charges are pulled to either contact where they establish compensating electric fields.…”