Wet Chemical Treatment and Mg Doping of p‐InP Surfaces for Ohmic Low‐Resistive Metal Contacts

Abstract

Manufacturing a low‐resistive Ohmic metal contact on p‐type InP crystals for various applications is a challenge because of the Fermi‐level pinning via surface defects and the diffusion of p‐type doping atoms in InP. Development of wet‐chemistry treatments and nanoscale control of p‐doping for InP surfaces is crucial for decreasing the device resistivity losses and durability problems. Herein, a proper combination of HCl‐based solution immersion, which directly provides an unusual wet chemical‐induced InP(100)c(2 × 2) atomic structure, and low‐temperature Mg‐surface doping of the cleaned InP before Ni‐film deposition is demonstrated to decrease the contact resistivity of Ni/p‐InP by the factor of 10 approximately as compared to the lowest reference value without Mg. Deposition of the Mg intermediate layer on p‐InP and postheating of Mg/p‐InP at 350 °C, both performed in ultrahigh‐vacuum (UHV) chamber, lead to intermixing of Mg and InP elements according to X‐ray photoelectron spectroscopy. Introducing a small oxygen gas background (O2 ≈ 10−6 mbar) in UHV chamber during the postheating of Mg/p‐InP enhances the indium outdiffusion and provides the lowest contact resistivity. Quantum mechanical simulations indicate that the presence of InP native oxide or/and metal indium alloy at the interface increases In diffusion.

Bridging the gap between surface physics and photonics

“…Measurements of wet chemically treated III-V and Ge surfaces [174][175][176][177][178][179] also support that Si( 111) is an unusual case because the post heating in UHV is typically needed to increase a crystalline order and the formation of atomically smooth terraces on the etched surfaces. Another difference between Si and III-V is that Si surfaces have typically hydrogen termination after the wet chemistry while III-V surfaces become enriched by group-V element in chemical treatments.…”

“…Extra group-V adsorbates can be removed at relative low temperatures in UHV [174][175][176][177][178]. For example, extra arsenic from GaAs at around 350 • C. However, recently it has been reported a surprising wet-chemically induced InP(100)c(2 × 2) surface which resembles atomically smooth Si (111), and which is expected to be hydrogen terminated after a proper HCl immersion [179]. Indeed, HCl-based etching solutions have been found to provide smoother surfaces for III-V and Ge, as compared to the F-containing wet chemistry [174][175][176][177][178][179][180].…”