A Comprehensive Investigation of HCl ‐ and Br2 /  NH 3 ( aq )  ‐ Etched p ‐ InP Interfaces

Abstract

The physical and chemical composition of p-InP surfaces prepared with HC1 and Br2/NH3(aq) etches have been investigated using SEM and XPS, and the interfacial energetics have been studied using capacitance and open-circuit photovoltage measurements. The Br2/NH3(aq) etch produced a microscopically smooth surface with a surface layer containing less than a monolayer of impurities, composed primarily of InPO4 with some In(OH)3 and some adsorbed hydroxyl species. The HC1 etch produced a rough, crystalline surface with a one to two monolayer indium-rich surface layer which was heavily hydrated and contained In20~ or In(OH)3 and adsorbed hydroxyl species. The HC1 etch also resulted in greater surface hydrocarbon contamination than the Br2/NH3(aq) etch. Capacitance measurements of the p-InP/acetonitrile interface reveal that the interfacial energetics of Br2/NH3(aq) etched electrodes are controlled by filling of empty surface states by solution redox couples, while those of the HCl-etched electrodes are controlled by electrochemical growth of a surface film. The BrJNH3(aq) etch yields a p-InP surface which allows efficient electron transfer to the solution resulting in a deep depletion energetic condition under extreme reverse bias conditions, while HCl-etched electrodes enter an inversion region where excess electrons accumulate in the space charge region. Empty surface states in the bandgap of Br2/NH3(aq)etched electrodes were found to be evenly distributed at a density of ca. 1.7 • 1012 cm -2 V -1. The open-circuit photovoltages of Br2/NH3(aq)-etched electrodes approached the bulk recombination limited value of 800 mV for redox couples with E(0') near -1.0V, but for the most negative and the most positive redox couples, deviations in the ~xpected behavior were observed. These are explained by bandedge movement which alters the barrier height. These studies reveal that the behavior of p-InP photoelectrochemical cells is determined largely by the method of surface pretreatment and only in part by bulk properties of the semiconductor material. Even when the surface films are only a few monolayers thick, their effect on the surface energetics are dramatic.

Theoretical and Experimental Upper Bounds on Interfacial Charge-Transfer Rate Constants between Semiconducting Solids and Outer-Sphere Redox Couples

“…Use of the manufacturer-reported dopant density N A = 1.1 × 10 17 cm -3 to calculate a barrier height for this system yielded φ b = 1.16 V. This value is in reasonable agreement with previous differential capacitance vs potential measurements on p-InP samples of slightly different dopant densities. These previous measurements yielded φ b = 1.23 V ( N A = 1.86 × 10 18 cm -3 ) or φ b = 1.03 V ( N A = 1.87 × 10 16 cm -3 ) 6 (a) C diff -2 vs applied dc potential for the p-InP/CH 3 CN−Co(Cp) 2 +/0 junction in Figure .…”

“…were essential to obtaining highly reproducible data having minimal frequency dispersion. This minimal frequency dispersion contrasts with prior reports of the impedance properties of many of these same photoelectrode systems, which apparently contained nonlinearities and/or frequency-dependent features that arose from an unoptimized experimental configuration of the cells and measurement apparatus and/or unoptimal electrode etching and surface preparation. − The InP/KCl(aq)−Fe(CN) 6 3-/4- cells consisted of 0.100 M Fe(CN) 6 3- , 0.100 M Fe(CN) 6 4- , and 1.00 M KCl, while p-InP/CH 3 CN−Co(Cp) 2 +/0 cells consisted of 0.0010 M Co(Cp) 2 , 0.020 M Co(Cp) 2 + , and 0.70−1.00 M LiClO 4 .…”

“…Further evidence for the presence of a chemical reaction between InP and KCl(aq)−Fe(CN) 6 3-/4- was obtained by investigation of the J − E properties of n-InP electrodes in contact with acidic HCl(aq)−Fe(CN) 6 3-/4- electrolytes (Figure ). In and P oxides are soluble in strongly acidic solutions of HCl(aq), ,− implying that active etching, as opposed to formation of an insoluble insulating oxide overlayer, should occur under these acidic conditions. In accord with these predictions, the J − E behavior of n-InP/HCl(aq)−Fe(CN) 6 3-/4- junctions at pH = 0 showed a significant open-circuit voltage, with V oc ≈ 400 mV (Figure b).…”

Optimized cleaning method for producing device quality InP(100) surfaces

“…HCl has also been used extensively on InP(100) surfaces, but mostly for etching [15 -20 ] rather than as a chemical cleaning method. Oxide and carbon contamination are reported on the surface after HCl etching [18]. This result should not be due to the chemical reactions of InP with the HCl, but rather environmental contamination after the etching, since these experiments were not done in a inert environment.…”

Effects of BCl3Passivation on Pt/Al/n-InP Diodes

“…Figure 4(d) shows the Cl 2p peak at 199.3 eV binding energy, which clearly reveals chlorine in chloride form, and it was suggested to be InCl 3 . 18,19) The detection of boron had been performed in the ESCA survey scans of the BCl 3 passivated InP substrate, while no obvious energy peak of boron was observed. Figure 5 shows the in-depth SIMS profiles of the BCl 3 passivated Pt/Al/n-InP diode after annealed at 300 C for 10 min.…”