Single Crystal Gallium Nitride Nanomembrane Photoconductor and Field Effect Transistor

Abstract

We report in this work the fabrication of single crystal GaN nanomembranes, with a thickness as low as 50 nm. Large area (≥5 mm × 5 mm) GaN membranes are produced by electrochemical etching (ECE) with a special high-conductivity sacrifi cial underlayer. Large-area, crackfree transfer of GaN NMs have been performed onto metal, glass, and polymer target substrates. The transport properties of freestanding GaN nanomembranes are analyzed using UV-assisted Hall measurements. The interaction of the carriers with the surface electronic states are investigated by the intensity dependence of the photoconductor gain, and by the temperature-dependent measurements of photocurrent decay. The transport property of GaN NM, down to a thickness of 90 nm, remains very comparable to that from much thicker GaN structures. Enhancement-mode fi eld effect transistors (FETs) have been fabricated and demonstrated on a SiO 2 / Si(001) wafer, suggesting that GaN nanomembranes can be a new candidate for fl exible electronics requiring high power and high-frequency. Results and Discussion Nanomembrane FabricationThe principle of using an ECE process to selectively remove underlying GaN sacrifi cial layers has been described before. [ 12,13 ] Multi-layered GaN structures having nanomembrane layers (50 to 500 nm thick) on top of heavily-doped ( n ≈ 1 × 10 19 cm −3 ) GaN sacrifi cial layers were grown by metal-organic chemical vapor deposition (MOCVD) process on sapphire. To obtain large-area NM within a reasonable time, a periodic array of via holes were created such that the undercut etching can proceeds uniformly around these openings. The via-holes are squares with a dimension of 10 µm and a diagonal periodicity of 25, 50, and 100 µm. These holes were created by Cl-based inductively coupled plasma (ICP) etching to expose the sacrifi cial layer. The photoresist (Shipley S1827) used during the Cl-ICP etching was retained to protect the front surface of the membrane during ECE. The nanomembrane layers became detached from the substrate once the undercut regions around each opening coalesce with the adjacent ones. GaN NMs were cleaned by rinsing sequentially in DI water, acetone and isopropyl-alcohol (IPA). After cleaning, they were transferred on to other substrates Single Crystal Gallium Nitride Nanomembrane Photoconductor and Field Effect Transistor Kanglin Xiong , Sung Hyun Park , Jie Song , Ge Yuan , Danti Chen , Benjamin Leung , and Jung Han * Large-area, free-standing and single-crystalline GaN nanomembranes are prepared by electrochemical etching from epitaxial layers. As-prepared nanomembranes are highly resistive but can become electronically active upon optical excitation, with an excellent electron mobility. The interaction of excited carriers with surface states is investigated by intensity-dependent photoconductivity gain and temperature-dependent photocurrent decay. Normally off enhancement-type GaN nanomembrane MOS transistors are demonstrated, suggesting that GaN could be used in fl exible electronics for high power and hig...

Gallium Nitride Crystals: Novel Supercapacitor Electrode Materials

“…All the GaNMM samples exhibit a broader peak width than GaNAG sample for (002) and (102) diffraction planes. This result is consistent with those in previous reports, which is likely due to the small thickness of the GaNMM in comparison with GaNAG . The larger FWHM can be explained by Scherrer's equation: Δ ω = λ / d cos θ , where λ is the wavelength of X‐ray, Δ ω is FWHM of the peak, and d is the thickness of crystal.…”

“…Preparation of Single‐Crystal GaNMM : Si‐doped GaN ( n = 5 × 10 −18 cm 3 , μ = 190 cm 2 V −1 s −1 ) was grown by MOCVD. The n‐type GaN samples were electrochemically etched according to a recently reported procedure . 0.3 m , 0.1 m , 0.05 m oxalic acid solutions were used as the electrolyte.…”

Morphology Controlled Fabrication of InN Nanowires on Brass Substrates

“…Furthermore, these single crystalline substrates are rigid, and the epilayers must be transferred to other substrates such as polyimide or metals in the fabrication of flexible (opto)electronic devices [26,27,28]. However, due to the high mechanical strength and chemical inertness of III-nitrides, separating them from the substrates is very difficult and time consuming [29,30,31,32]. …”

(Invited) Applications of Electrochemistry for Novel Wide Bandgap GaN Devices

“…Depending on the layer conductivity and applied bias, the EC etching may cause no effect, nanoscale porosification, or complete etching of GaN (7). The EC etching has been applied to different areas of GaN material and device technologies, including layer separation, the preparation of flexible GaN membrane devices, and the formation of distributed Bragg reflector (DBR) for photonic applications (8,9,10).…”