Wet chemical etching of AlN in KOH solution

Abstract

In this work we investigated the influence of the AlN material quality on the etching rate in KOH-based solutions. Thus, AlN layers were deposited by three different methods on sapphire and silicon substrates (i) by metal organic chemical vapor deposition (MOCVD), (ii) by molecular beam epitaxy (MBE), and (iii) by reactive sputter deposition. The etch rate is strongly dependent on crystal quality and etch temperatures. The high quality MBE-AlN could be etch anisotropic with a preferred lateral component in [ ]1120 direction at 60 °C while the polycrystalline AlN layers we etched isotropic and homogenously already at room temperature. The wet chemical etching in KOH solution is mainly an etching along defects and grain boundaries.

Micro‐ and nano‐electromechanical resonators based on SiC and group III‐nitrides for sensor applications

“…To achieve free‐standing AlGaN/GaN MEMS, a selective etching technique for AlN sacrificial layers was developed. KOH‐based wet etching of AlN with a different crystalline quality resulted in a strong lateral etching for single‐crystalline substrates, and in isotropic etching for nano‐crystalline layers 103. NaOH‐based solutions showed a preferential lateral etching as well, at much lower etch rates but with a considerably increased selectivity to the AlGaN/GaN layers than for KOH‐based solutions.…”

“…In case of sapphire, a sputtered nano‐crystalline AlN layer with a thickness of 500 nm served as a sacrificial layer. Due to its in‐plane and vertical alignment, it allowed epitaxial overgrowth, and its nano‐crystalline structure enabled selective etching 103.…”

“…17. Biocompatibility tests have shown an excellent suitability of AlN, which also provides adhesion without any adhesive agent 103. The mass loading of Δ m = 1.5 ng led to a significant frequency shift corresponding to S m = 0.24 kHz/pg 109.…”

Space charge limited electron transport in AlGaN photoconductors

“…Since the Auger peak position is sensitive to the position of the Fermi level, 36 the Auger peaks from p-, n-, and i-AlGaN layers could be distinguished, although the concentration of the dopands is much lower than the detection limit of AES. The position of the equilibrium Fermi level in i-Al 0.5 Ga 0.5 N ͑E C E F 0 ϳ 1.76 eV͒ has been determined from AES peak shift using the reference peak position provided by a n-doped ͑n e ϳ 2 ϫ 10 16 cm −3 ͒ Al 0.5 Ga 0.5 N : Si sample.…”

Fully unstrained GaN on sacrificial AlN layers by nano‐heteroepitaxy

“…In this paper, we report on the nanoheteroepitaxy (NHE) of unstrained high quality epitaxial GaN layers and AlGaN/GaN heterostructures by metal-organic vapor deposition (MOCVD) on templates consisting of thick sputtered nanocrystalline AlN on sapphire. AlN can be removed selectively to GaN by wetchemical etching techniques [3] and, thus, is suitable as sacrificial layer. The resulting structures combine the advantages of a novel sacrificial layer technique with the possibilities of an AlGaN/GaN heterostructure with an inherent 2D elecron gas (2DEG).…”