Chemical studies of the passivation of GaAs surface recombination using sulfides and thiols

Abstract

Steady-state photoluminescence, time-resolved photoluminescence, and x-ray photoelectron spectroscopy have been used to study the electrical and chemical properties of GaAs surfaces exposed to inorganic and organic sulfur donors. Despite a wide variation in S2-(aq) concentration, variation of the pH of aqueous HS-solutions had a small effect on the steady-state n-type GaAs photoluminescence intensity, with surfaces exposed to pH = 8, O.l-M HS -(aq) solutions displaying comparable luminescence intensity relative to those treated with pH = 14, 1.0-M Na2S*9H20( aq). Organic thiols (R-SH, where R = -CH2CH2SH or -C6H4C1) dissolved in nonaqueous solvents were found to effect increases in steady-state luminescence yields and in time-resolved luminescence decay lifetimes of ( lOO)-oriented GaAs. X-ray photoelectron spectroscopy showed that exposure of GaAs surfaces to these organic systems yielded thiols bound to the GaAs surface, but such exposure did not remove excess elemental As and did not form a detectable As2S, overlayer on the GaAs. These results imply that complete removal of As0 or formation of monolayers of AZ@, is not necessary to effect a reduction in the recombination rate at etched GaAs surfaces. Other compounds that do not contain sulfur but that are strong Lewis bases, such as methoxide ion, also improved the GaAs steady-state photoluminescence intensity. These results demonstrate that a general class of electrondonating reagents can be used to reduce nonradiative recombination at GaAs surfaces, and also imply that prior models focusing on the formation of monolayer coverages of As2Ss and Ga2S3 are not adequate to describe the passivating behavior of this class of reagents. The timeresolved, high level injection experiments clearly demonstrate that a shift in the equilibrium surface Fermi-level energy is not sufficient to explain the luminescence intensity changes, and confirm that HS -and thiol-based reagents induce substantial reductions in the surface recombination velocity through a change in the GaAs surface state recombination rate.

Fabrication of radial superlattices based on different hybrid materials

“…[3]), indicates that the thiol successfully protects the semiconductor layer against oxidation. The highly effective protection and passivation of GaAs surfaces by molecular self-assembled monolayers has been studied in detail previously [19]. Furthermore, in the case of a rolled-up radial superlattice, the hydrophobic nature of the thiolated GaAs possibly suppresses the incorporation of water from the wet chemical etching solution into the tube walls.…”

A model for emission yield from planar photocathodes based on photon-enhanced thermionic emission or negative-electron-affinity photoemission

“…3 illustrates that passivation of the emissive surface may noticeably boost emission yields in conventional photocathodes, as surface recombination velocities on the order of 10 3 -10 4 cm/s are readily achievable in GaAs that has been passivated chemically or by AlGaAs or GaInP. [31][32][33] This largely unexplored route to increasing efficiency may be fruitful in practice because commonly used cesium-based surface coatings typically degrade over time in ultra-high vacuum systems, consequently decreasing emission probability and hence device performance. Reducing the surface recombination velocity through passivation would mitigate this decay in emission yield during this degradation process.…”

Influence of Thiol Coupling on Photoluminescence of Near Surface InAs Quantum Dots

“…However, effects of the surface modification on the luminescence properties have been discussed in terms of increased PL intensity and PL decay time only for bulk GaAs [15,16]. In previous studies, we demonstrated the electrochemical stabilization of the GaAs surface by the ODT monolayer deposition in aqueous electrolytes [2].…”