Photopotential Measurements on Undopedn-InP at Open Circuit Potential According to the Aqueous pH

Abstract

In this work we studied some fundamental concepts of n-InP interfacial properties based on acid-base equilibrium in the dark and also after the surface illumination at open circuit voltage (Voc). The variation of the flatband potential on undoped n-InP semiconductor was investigated according to aqueous pH. This study was complemented by the effect of the illumination at Voc conditions through photopotential measurements. The impact of the surface lighting on acid-base equilibrium was analyzed by in-situ interfacial capacitance measurements in the dark and by ex-situ X-ray photoelectron spectrometry. The fundamental properties of many semiconductor/electrolyte systems were monitored by the flatband potential position (E FB ). 1,2Its position governed the interfacial characteristics and controlled the electrochemical properties. A classical way of measuring the variation of the flatband potential position was to change the pH of the medium. Many semiconductors were actually sensitive to the variation of acid-base equilibrium.3-12 For III-V semiconductors such as binary (GaAs 3,5 or GaP 6,7 ) or ternary 8 compounds, the acid-base equilibrium was complicated by the specific adsorption sites which induced localized charges on the surface. 13 Previous works have shown a quasi Nernstian variation of the flatband potential on n-InP for (100) 14 and (111) faces 13 over the whole pH range in aqueous medium and also in non aqueous medium such as acetonitrile 15 and liquid ammonia. 16Acid-base equilibrium was studied in the dark from interfacial capacitance measurements in the depletion region avoiding faradaic transfer at the interface semiconductor/electrolyte. This included changing the voltage of the semiconductor artificially through the use of a potentiostat. The band bending owing to electron depletion in the semiconductor (SC) changed depending on the voltage. In the depletion region the Boltzmann relation described the distribution of electrons in the space charge region and the electric field was determined by Gauss'law. Poisson's equation could be solved within that region to give the Mott-Schottky equation that links the reverse square of the capacitance (C) to the interfacial polarization (E). 17 Under depletion conditions the flatband potential was actually deduced from C −2 = f(E) straight line which extrapolation gave E FB for a zero value of C −2 . There are other ways to evaluate the flatband potential such as measuring the photopotential at the open circuit voltage (Voc). As a function of radiation intensity the photopotential was the change in the Fermi level due to the promotion of electrons to the conduction band, and it reached theoretically a maximum at the flatband potential. 13,18 In this paper acid-base equilibrium were further discussed on undoped nInP in which the low doping level led to a space charge region strongly different as compared to high doped n-InP. 9,[13][14][15][16]18 This was particularly true in terms of surface electrical field, charge, capacitance, layer of the space charge re...

Band Alignment of n- and p- InP at Electrolyte and Ultra High Vacuum Intrefaces: Correlation between the Open Circuit Potential under Illumination and XPS Photopeak Energy Separations

“…Note that in this case the electrolyte is diluted with sulfuric acid (0.5M), which maintains a perfect oxide free interface. This gives rise to a perfect reversibility of Voc between the dark and illuminated situations contrary to observations which have been already studied in neutral pH (7).…”

Unique Porous Structures Supported by Anodic Treatments in Liquid Ammonia (-50°C, Patm)

“…After ammonia condensation the semiconductor was immersed in the electrochemical cell which was kept at low temperature (-55°C) in a cryostat at atmospheric pressure. The illumination of III-Vs was performed thanks to the use of an optical fiber which was connected to a led light engine using Schott KL 2500 Led (14). Ammonium bromide with a concentration of 0,1 M, (purest available quality from Aldrich) was added to the medium.…”

(Invited) Outstanding Contributions of Liquid Ammonia on III-V Semiconductors (Photo)-Electrochemistry

“…After ammonia condensation the semiconductor was immersed in the electrochemical cell which was kept at low temperature (-55°C) in a cryostat at atmospheric preasure. The illumination of III-Vs was performed thanks to the use of an optical fiber which was connected to a led light engine using Schott KL 2500 Led (7). Ammonium bromide with a concentration of 5.10 -3 M, (purest available quality from Aldrich) was added to the medium.…”

“…The first reduction step was mono-electronic and led to the formation of the radical O 2 .- [6]. The second step led to the formation of O 2 2- [7].…”