Plasma-assisted oxide removal from p-type GaSb for low resistivity ohmic contacts

Abstract

The effect of several plasma-assisted oxide removal techniques prior to metallization of p-type GaSb was investigated. Compared to conventional chemical methods, the plasmaassisted oxide removal resulted in significant improvement of the specific contact resistivities, obtained from transfer length method measurements. Very low specific contact resistivities of less than 5 × 10 -8 Ω cm 2 were observed after surface pre-treatment by H2/Ar sputter etching and low-ion-energy argon irradiation. By eliminating sample exposure to air, in-situ Ar irradiation becomes a promising technique for high performance GaSb-based semiconductor diode lasers.

Aluminum-based contacts for use in GaSb-based diode lasers

“…It is one of the lowest reported results for contact to ptype GaSb(001). However, it is also quite a bit below the lower limit (5 × 10 -8 Ω cm 2 in this case 3 ) for accurate/valid results of the measurement method, and thus there is a relatively high uncertainty attached to this value. This is supported by the fact that the measurements of two out of three annealed Al samples gave negative contact resistances (Rc) with small absolute values similar to the positive contact resistance of the third sample, indicating that the TLM failed to determine accurately the extremely low specific contact resistivity of the Al contact to p-type GaSb after annealing.…”

“…The metallization of the laser contacts presented in Figure 2 and Table II were performed as in the specific contact resistivity experiments, except using an optimized Ar ion energy of 180 eV to remove GaSb native oxide 3 . To achieve good bonding to the aluminum contact, 50 nm of SiO2 was added to improve the adhesion between photoresist and Al.…”

“…To determine the specific contact resistivity of Al-based contacts, the transfer length method (TLM) and four-probe measurements were performed on samples grown by molecular beam epitaxy (MBE) 3,17 . For the contacts to p-type GaSb(001), a 2 µm thick epitaxial layer of Be-doped GaSb was grown on a 100 nm thick undoped GaSb buffer layer grown on n-type GaSb(001) wafer (with nominal carrier concentration of 5 × 10 17 cm -3 ) in a solid source Varian GEN II Modular MBE system.…”

“…TLM structures were defined by conventional UV-lithography and were isolated on rectangular mesas by Inductively-Coupled Plasma -Reactive Ion Etching (ICP-RIE) 3 . The metallization was performed by e-beam evaporation in a combined sputtering and e-beam evaporation system (AJA ATC-2200V) at a starting pressure of 10 -7 Torr.…”

Dopant incorporation in Al 0.9 Ga 0.1 As 0.06 Sb 0.94 grown by molecular beam epitaxy

“…Be-doped GaSb) of the sample using conventional photolithography. Prior to metallization, GaSb surface oxide was removed in situ by Ar sputtering at 325 eV in a combined sputtering and e-beam evaporation system (AJA ATC-2200V) [19]. A Ti/Pt/Au (50 nm/25 nm/325 nm) metal stack was deposited using e-beam metal deposition followed by a metal lift-off by acetone to define front contact pads.…”