Chemical Etch Characteristics of N-Face and Ga-Face GaN by Phosphoric Acid and Potassium Hydroxide Solutions

Abstract

We report the chemical etching characteristics of Ga-face and N-face GaN using phosphoric acid (H 3 PO 4 ) or potassium hydroxide (KOH) solutions. Hexagonal pyramids, which consisted of the {10-1-1} planes, were present on the N-face after KOH (2M, 100 • C) etching. By contrast, using the H 3 PO 4 (85 wt.%, 100 • C) solutions, the nitrogen surface of GaN showed dodecagonal pyramids. Dodecagonal and hexagonal pyramids repeatedly appear on the etched surface when using the H 3 PO 4 or KOH solutions, respectively. A low concentration of H 3 PO 4 (H 3 PO 4 : deionized water = 1:32, 1:64) produced a roughened surface with coexistence of dodecagonal and hexagonal pyramids. The photoluminescence (PL) intensity of the etched surfaces significantly increased due to multiple scattering events compared to the non-etched surface. Thus, the etching techniques developed in this study were shown to improve the light extraction efficiency of light emitting diodes (LEDs), avoiding the damage to the GaN typically created by plasma etching methods.

Effect of etching with cysteamine assisted phosphoric acid on gallium nitride surface oxide formation

“…This observation confirms qualitatively the Gaface character of the GaN surface, as no prominent pyramidal structures can be seen. 14,15,25,26,32 The RMS surface roughness for the free-standing bulk GaN surface was found to be 3.4 6 1.2 nm, which increased to 3.9 6 1.1 nm and 9.1 6 6.5 nm, respectively, after etching with phosphoric acid with and without cysteamine at 40 C. Increasing the temperature treatment to 100 C resulted in decreased roughness to 2.7 6 0.9 nm after treatment with cysteamine, but increased roughness to 13.3 6 6.9 nm after 100 C treatment without cysteamine. Comparing only the effect of treatment in solutions without cysteamine, the surface roughness increases with higher temperature.…”

“…Alternatively, the surface can be etched (via heated KOH [13][14][15] or phosphoric/sulfuric 14,16 acid) or coated with thiols, 17 or other molecules. [18][19][20][21][22][23] The etching and surface functionalization routes provide convenient ways to modify GaN surface properties without the need for intensive doping strategies that predominantly rely on hazardous chemicals.…”

Comparison of the Stability of Functionalized GaN and GaP

“…[9,25,26] Their natural stability provides a platform for chemical sensors, [27] solar technology, [28] and biological sensors. [29,30] Fabrication for GaN and GaP applications is limited to extreme acidic and basic conditions [31] as well as energetically driven environments [32,33] via etching solutions of molten KOH, [34] NaOH, [32] phosphoric acid, [35] sulfuric acid, [26] or nitric acid. [36,37] Increased complexity is added due to the different stabilities between group III and group V atoms, which leads to preferential removal of group V atoms to form group III-rich crystallographic features.…”

“…ing mechanism for GaN can be seen in Equation (1): [34] The formation of ammonia provides the primary mechanism of crystal attack and subsequent isolation of insoluble gallium oxide (Ga 2 O 3 ). Ga 2 O 3 is the primary oxide formed for gallium in neutral solutions, whereas ionic species of Ga 3 + , HGaO 2 2À , and GaPO 4 provide paths for gallium solubility in acidic environments.…”

Research on N-face GaN for solar cells based on MOCVD method

“…A large number of dodecagonal pyramidal structures are formed. In N-face GaN, there is only one dangling bond point to surface of N atoms, thus the Ga atom is easy to react with acid solution, formed Ga 2 O 3 , then dissolved in acid solution [12]. H 3 PO 4 plays a role of catalyst and the dissolution agent of Ga 2 O 3 also.…”