PtTiPtAu and PdTiPtAu ohmic contacts to p-InGaAs

Abstract

1Onm layers of Pt and Pd were employed as an interlayer between Ti(30nm)Pt(SOnm)Au(2OOnm) metallization and p-InGaAs doped at 1-4~10'~cm". For the annealing temperatures of 30O-50O0C, the F'tTiPtAu and the PdTiF'tAu metallizations exhibited consistently lower contact resistivities than the TiF'tAu metallization. The effective barriers height of the PtTiPtAu contacts (0.1 l e v ) was estimated to be lower than those of the PdTiF'tAu contacts (0.14eV) and the TiPtAu contacts (0.16eV). The high work function Pt lowered the barrier height. The Pd, on the other hand, formed a favorable interfacial compound when as-deposited, thereby reducing the contact resistivity.of InP based optoelectronic devices, Ino 5 3 G~ 47A~ doped over 1 x l OI9cme3 is used as a payer since it has the smallest band gap among InP lattice-matched materials. As for the pt metals, the TiPtAu metallization is, by far, the most popular. This metallization scheme ealing was reported to yield very low contact resistivities in the region of e InGaAs layers were invariably doped extremely high i.e. > l~l O~~c m " . ion was Katz et a1 [4]; they reported a contact resistivity of 3.4x10~*Rcm2 with InGaAs '9cm-3. In our experience, the contact resistivity of TiPtAu contacts to p-InGaAs doped -5!2cm2 while the same metallization formed ohmic contacts to p-GaAs .4-1 .lx10"Rcm2. The high contact resistivity with p-InGaAs should be related to the el pins in InGaAs -near the conduction band edge [5]. The n-type barrier height is -type, it is nearly the same as the entire band-gap, making it difficult to form low between a p-type semiconductor and a metal is the difference in Schottky barrier height, a= a-cp, work fkction is used, the barrier height is reduced as the band bending , it would be possible to lower the contact resistivity. In this paper, the role n metals, Pt (Qm=5.65eV) and Pd (Qm=5.12eV), was investigated as an :s and TiPtAu metallization. The work function of Ti is 4.33eV.were grown on Fe-doped semi-insulating InP using metalorganic vapour itaxy (MOVPE). Three different Zn doping concentrations -1x1 0'9cm-3, 2~1 0 '~c m -~, 4~1 0 '~c mrepared to study the current transport mechanism. Prior to metal deposition, the InGaAs layers ated with buffered oxide etchant for 10 seconds to remove oxides. The basic metallization nm)Au(2OOnm), but a lOnm Pt or Pd interlayer was included between the le InGaAs. The results were compared to the one with no interlayer. The

Selective Deposition of Ohmic Contacts to p-InGaAs by Electroless Plating

“…The addition of a thin Pd first layer to a Ti/Pt/Au metallization can dramatically reduce the contact resistance to p-InGaAs. 10 We have also found Pd to produce low contact resistances on p-InAs 11 and p-InAsP. 12 On GaAs, Pd has been shown to penetrate the native oxide and form a more intimate metal/ semiconductor interface.…”