Anodic Dissolution and Selective Etching of Gallium Phosphide

Abstract

Current voltage curves and the effective dissolution valence have been determined for GaP electrodes in 3N NaOH solution. At electrode potentials of a few volts the current density for p-type (NA ~ 4(10)17-cm-3) is a factor of 10 4 greater than for n-type (ND ~ 4 (10)17 cm-3) electrodes. This difference allows selective removal of p material from p-n structures. Application of this selective etching to the fabrication of mesa structures for GaP light emitting diodes, and to junction delineation, is discussed. At large current densities, 6 charges are transferred per dissolved GaP molecule in distinction to the 3 transferred charges found previously in alkaline solution at low (< 2mA cm -~) current densities.As III-V compound semiconductor device technology is advanced, it becomes desirable to apply some of the electrochemical processing and evaluation techniques which have proven useful for silicon and germanium (1-3) to those materials. The present paper discusses anodic dissolution and selective etching of gallium phosphide.In comparison to germanium and silicon, the electrochemistry of the III-V compounds has not been widely studied. The occurrence and nature of surface films (4, 5) and the morphology of the etched surface (5, 6) have been determined for InSb. Several authors have discussed the electrochemistry (7-12) and Nuese and Gannon have described selective etching (13) of GaAs. Memming (14, 15) has studied GaP, but not at the rather large anodic current densities desired for etching and shaping operations.Experimental Current density-potential relations were determined in the apparatus of Fig. 1. The electrolyte was 3N aqueous NaOH maintained at 20~ although the exact temperature is not critical. Measurements were made in the dark and potentials are relative to the saturated calomel reference electrode. The samples were of (111) orientation, and both the Ga (111) and P-(lil) faces were studied. The faces were distinguished by their chemical etching characteristics in C12 saturated methanol. This and equivalent techniques are ultimately traceable to x-ray evidence. N-type samples were Se doped and p-type samples were Zn doped to a level of about 4(10) 17 cm -8 and were cut from LEC (Liquid Encapsulated Czochralski) pulled ingots. Ohmic contacts on p-type (n-type) were prepared by evaporating and alloying gold containing 1% Be (2% Si). Surfaces were chemically or mechanically polished, as applicable, before use as electrodes. The number of electronic charges passing through the external circuit per dissolved atom was determined by integrating the current for a certain time and measuring the weight loss with a microbalance.

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.…”

“…[46] Regions not capped with functional groups were used to test the leaching capacity of hydroxyl groups versus subsequent oxide formations such as gallium sub-oxides [GaO(OH), Ga 2 O, GaO] and amorphous gallium oxide (Ga 2 O 3 ). [33] In addition to analyzing patchy regions, the use of hydrogen peroxide Scheme 1. Surface stripping, etching, functionalization, and capping of GaN and GaP.…”

A kinetic study of structured surface relief patterning of GaP $$(\bar 1\bar 1\bar 1)$$

“…23 According to Gatos and Lavine for ideal (111) surfaces, the surface A atoms (Ga) are characterized by unoccupied dangling bonds at the surface, while the B atoms have fully occupied sp 3 electrons which can easily participate in chemical reactions. Usually, the faces are distinguished by their chemical characteristics in halogen (for example Cl 2 ) saturated methanol 15 or in hot aqua regia. 5,23 Different solutions have been used to identify A and B surfaces in GaP.…”

“…[1][2][3][4][5] The majority of publications in this area are dedicated to etching of GaAs and InP, rather than GaP. 15 It was shown that controllable etching of ( 1 1 1 ) GaP with H 3 PO 4 was only possible for etching rates between 5 and 25 µm/min. However, there have been few reports on etching of GaP.…”

Photoanodic Dissolution Reaction of an n‐Type Gallium Phosphide Electrode and Its Effect on Energies of the Electronic Bands at the Surface

“…It was reported that six holes are consumed per a pair of Ga and P atoms in the photoanodic dissolution reaction at both the (111)-and (lll)-faces, probably producing Ga(OH)s and H3PO3 or their analogues (11,(13)(14)(15). Also, the formation of a layer of hydroxides or oxides of Ga and P is often assumed for explaining quite hysteretic photocurrent-potential curves or production of white films on the electrode surface, especially in the intermediate pH range (10,13,14,16).…”