Low-optical-loss, low-resistance Ag/Ge based ohmic contacts to n-type InP for membrane based waveguide devices

Abstract

We present the development of Ag/Ge based ohmic contacts to n-type InP with both low contact resistances and relatively low optical losses. A specific contact resistance as low as 1.5×10 −6 Ω cm 2 is achieved by optimizing the Ge layer thickness and annealing conditions. The use of Ge instead of metal as the first deposited layer results in a low optical absorption loss in the telecommunication wavelength range. Compared to Au based contacts, the Ag based metallization also shows considerably reduced spiking effects after annealing. Contacts with different lengths are deposited on top of InP membrane waveguides to characterize the optical loss before and after annealing. A factor of 5 reduction of the propagation loss compared to the conventional Au/Ge/Ni contact is demonstrated. This allows for much more optimized designs for membrane photonic devices.

67 GHz uni-traveling carrier photodetector on an InP-membrane-on-silicon platform

“…2. (a) shows the measured dark current of 153 nA at -4 V. In order to determine the internal responsivity, the coupling loss from fiber to WGs is first measured on test WGs using a standard setup described in [5], and calibrated out. The responsivity versus wavelength is plotted in the inset of Fig.…”

A Novel Broadband Electro-Absorption Modulator Based on Bandfilling in n-InGaAs: Design and Simulations

“…Previous results of Au/Pt/Ti metalization for the p-contact and Au/Ge/Ni for the ncontact [13] have shown a specific contact resistance below 2 · 10 −6 Ω cm 2 . An adiabatic taper was designed to couple light from the waveguide to the device [14].…”

High-bandwidth uni-traveling carrier waveguide photodetector on an InP-membrane-on-silicon platform

“…As mentioned in Section 2, the n-contact is specially designed with a 20 nm thin layer of Au to reduce the spiking effect and thus giving low optical loss. In order to evaluate the loss from the n-contact, a propagation loss coefficient of 1.16 dB/µm is measured from testing WGs on this chip using an approach introduced in our previous work [23]. In that work, the loss coefficients of the standard NiGeAu n-contact (with a 300 nm thick Au layer) measured before and after annealing are 0.93 and 2.91 dB/µm, respectively.…”

“…Comparison of these results indicates that the optimized n-contact used here is indeed important for loss reduction. A GeAgbased n-contact proposed in [23] shows an even lower loss coefficient (0.56 dB/µm) and should therefore allow for a higher responsivity. The dark current measured for the 3×10 µm 2 UTC-PD is plotted in the inset of Fig.…”

“…The exponential behavior of the measured dark current suggests that the tunneling current might be dominant here. The dark current may be reduced by using the spiking-free n-contact based on GeAg [23]. The responsivities measured for several UTC-PDs are plotted in Fig.…”