A comparative study of GaSb (100) surface passivation by aqueous and nonaqueous solutions

Abstract

We report a nonaqueous passivation regime consisting of Na 2 S/benzene/15-crown-5/oxidant. The use of a nonpolar, aprotic organic medium required the addition of a specific chelating agent ͑15-crown-5͒ to solubilize sodium sulfide, and organic oxidizing agents ͑anthraquinone, benzophenone, etc.͒ to act as electron acceptors. The surface optical and chemical properties of GaSb surfaces after aqueous and nonaqueous sulfide treatments were compared. Nonaqueous passivation resulted in higher photoluminescence ͑PL͒ intensity, lower oxide content, and a less amount of elemental Sb than aqueous passivation. The PL intensity from passivated surfaces was correlated with the standard reduction potentials of electron acceptors. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1613994͔The surface properties of semiconductors are crucial determinants of device performance. Considerable efforts have been made to modify III-V semiconductor surfaces in order to improve electronic properties and device performance. The passivation of GaAs with aqueous solutions of sodium or ammonium sulfides has been extensively studied both theoretically and experimentally. [1][2][3][4] The reactions between chalcogenides and GaAs surface species change the surface electronic structures and remove the surface states from the band gap, thus unpinning the surface Fermi level and improving electrical and optical properties.GaSb is an important III-V compound semiconductor for high-speed and optoelectronic device applications, the performance of which is strongly dependent on the chemical and electronic properties of GaSb surfaces or interfaces. However, GaSb is highly chemically reactive, being easily oxidized by atmospheric oxygen with the formation of native surface oxides several nanometers thick.5 An additional consequence of surface oxidation is the formation of elemental antimony at the oxide-GaSb interface, which creates a conduction channel parallel to the interface that leads to high surface leakage current, thus limiting applications.6,7 Various surface passivation methods, including wet and dry chemical processes, [8][9][10][11] have been studied in efforts to improve GaSb surface characteristics. Unfortunately, most processing techniques are still water-based and lead to the growth of surface oxides and degrade the structural quality of the surface. Therefore, alternative, nonaqueous, solvents capable of sulfidization are of particular interest for GaSb surface processing.In this work, a specific benzene-based sodium sulfide passivation regime was developed to improve the passivation of GaSb surfaces. Chelating agents were employed to solubilize and activate sulfide anions, and organic oxidizing agents were added to the passivation solution to facilitate electron transfer. The optical and chemical characteristics, before and after chemical treatments, were studied by photoluminescence ͑PL͒ and x-ray photoemission spectroscopy ͑XPS͒. A comparison of the results of GaSb passivation in aqueous and nonaqueous sulfide solutions indicat...

Effect of surface treatment with different sulfide solutions on the ultrafast dynamics of photogenerated carriers in GaAs(1 0 0)

“…Therefore, the chemical properties of HS − ions in aqueous and in alcoholic solution will be principally different and the mechanism of interaction of such solvated ions with the semiconductor surface atoms should depend on the solvent. Besides, it was demonstrated that the presence of electron acceptors in the passivating sulfide solution is essential for electronic passivation of semiconductor surface [30]. In accordance with density functional theory calculations, the hydrated HS − ions (solvated by water molecules) have equal probability to donate and to accept electrons in the course of chemical reaction, whereas the water molecules forming the hydration shells around the HS − ions can neither accept nor donate electrons [31,32].…”

“…Some reduction of the surface recombination velocity in this case can be associated with the shift of the energy level of the surface state due to chemical interaction of this state with the hydrated HS − ion. By contrast, the HS − ions solvated by alcohol molecules can easily donate electrons but hardly accept them, while the alcohol molecules of the solvation shell can easily accept electrons [30,31]. Therefore, the alcohol molecules from the solvation shell can act as electronic acceptors and charge from the semiconductor surface states can be transferred to solvent molecules and will remain in the solution or go further to the gas phase (Fig.…”

Improved characteristics for Au∕n-GaSb Schottky contacts through the use of a nonaqueous sulfide-based passivation

“…Surface passivation using sulfide-based solutions can effectively remove the native oxide and improve the surface electronic and electrical properties. [5][6][7] Previous studies of the sulfurbased passivation using a ͑NH 4 ͒ 2 S-water solution have shown improved Schottky characteristics with a Au-GaSb barrier of 0.52-0.57 eV being reported. 8,9 The use of an aqueous process however, with and without S passivation, leads to a variety of results in the formation of a Au-GaSb Schottky diode with a wide range of the barrier height values being reported, even exceeding the band-gap energy.…”

“…The details of this process were described previously. 7 The performed surface treatments before Au deposition are summarized below:(a) Without further treatment after chemical degreasing; (b) Dipping in concentrated HCl for 5 min, then rinsing with 2-propanol; (c) Dipping in concentrated HCl for 5 min, rinsing with 2-propanol, then immersing in a saturated Na 2 S aqueous solution for 1 h, then rising with water; and rinse; (d) Dipping in concentrated in HCl for 5 min, rinsing with 2-propanol, then immersing in a benzene-based Na 2 S solution for 1 h, then rinsing with 2-propanol.The topside contacts were then fabricated by the e-beam deposition of Au onto the chemically treated roomtemperature GaSb sample surfaces. The contact area was defined by a shadow mask, and the diameter of the circular diode, ⌽, was 130 m. Between four and ten diodes were measured for each surface treatment.…”

“…Nonaqueous passivation using an inert solvent, such as benzene, as the sulfidization medium results in a GaSb surface with decreased amounts of oxide residue and elemental Sb content compared to that generated by aqueous sulfide treatment. 7 In this work, the impact of a nonaqueous S-based passivation treatment on the Au/ n-GaSb Schottky junction behavior was studied. In particular, a nonaqueous sulfide passivation process was applied before metalization, and compared with the aqueous sulfide treatment in terms of improving GaSb-based Schottky device performance.…”