Investigation of arsenic and antimony capping layers, and half cycle reactions during atomic layer deposition of Al2O3 on GaSb(100)

Abstract

In-situ monochromatic x-ray photoelectron spectroscopy, low energy electron diffraction, ion scattering spectroscopy, and transmission electron microscopy are used to examine the GaSb(100) surfaces grown by molecular beam epitaxy after thermal desorption of a protective As or Sb layer and subsequent atomic layer deposition (ALD) of Al2O3. An antimony protective layer is found to be more favorable compared to an arsenic capping layer as it prevents As alloys from forming with the GaSb substrate. The evolution of oxide free GaSb/Al2O3 interface is investigated by “half-cycle” ALD reactions of trimethyl aluminum and deionized water.

Oxidation of GaSb(100) and its control studied by scanning tunneling microscopy and spectroscopy

“…Atomic scale STM images together with the STS analysis reveal that the initial stages of oxygen incorporation lead to the formation of unoccupied defect states in the upper part of the gap. When coupled with the previous XPS findings, 9 we suggest that the initial stages of oxidation of GaSb(100)(4 Â 3) includes the substitution of second-layer Sb by O and the subsequent Sb enrichment on the surface, which is detrimental to the quality of GaSb-based interfaces. To reduce harmful effects of the GaSb oxidation, we report a method to prepare the GaSb(100)(4 Â 2)-In surface and oxidize it into the form of previously unreported phase of crystalline oxidized (1 Â 3)-In-O.…”

“…The previous [4][5][6][7][8][9][10]14 and current findings indicate that the Sb concentration at the GaSb surface (interface) should be minimized to decrease the amount of defect states at insulator/GaSb interfaces. It appears that the problem is not the formation of Sb 2 O 3 itself (or other Sb-oxide phase) because the Sb 2 O 3 band gap is 3-4 eV.…”

“…2 Gallium antimonide (GaSb) has attracted an increasing interest as for the channel material of future MOS transistors, in particular, due to a superior mobility of holes in GaSb. [4][5][6][7][8][9][10][11][12][13][14][15][16][17] The GaSb oxidation at the insulator interfaces such as atomiclayer-deposited (ALD) Al 2 O 3 /GaSb and HfO 2 /GaSb has been found to cause various oxidation states of GaSb including Ga 2 O, Ga 2 O 3 , Sb 2 O 3 , and/or Sb 2 O 5 according to x-ray photoelectron spectroscopy (XPS) measurements. 10,18 By obtaining interrelationship between the interfacial chemistry from, for example, XPS measurements and capacitance-voltage (C-V) characterization of the same interfaces, the effects of the oxidation states on the electrical properties of the interfaces have been clarified: it is interesting that neither Ga 2 O 3 -nor Sb 2 O 3type interface phase is necessarily harmful to the electrical performance.…”

“…However, it can be expected that at lower temperatures (e.g., 200-300 C used in ALD), Sb remains on the surface but is not initially oxidized. 9 This implies that metallic Sb can be enriched on the surface due to the oxidation process.…”

GaSb oxide thermal stability studied by dynamic-XPS

“…Such oxides can inhibit subsequent epitaxy and also be a source of traps for devices as a result of defect levels in the energy gap. 2,9 To achieve this, capping the surface 10 and high temperature annealing in ultrahigh vacuum (UHV) 11,12 or other reducing ambient, such as atomic hydrogen, 3,12,13 is often employed. This process has been examined in previous works but is revisited in this study with dynamic-x-ray photoelectron spectroscopy (dynamic-XPS) where the remarkable temperature resolution combined with multichannel photoelectron data acquisition enables a detailed study of the initial decomposition of the native oxide in real time.…”