Abstract

We report on work concerned with the optoelectronic properties of a GaAs optical waveguide containing a resonant tunneling diode (RTD).¹ As far as we are aware this is the first report of an RTD directly incorporated in an optical waveguide and the observation of optical modulation via a Franz-Keldysh shift on the band edge. Figure 1 shows a cross-section schematic of the device. The device that was employed for our Franz-Keldysh band-shift measurements consisted of a 4-μm-wide optical waveguide with a 200-μm-long contact on top of the waveguide defining an active area of 800 μm². Figure 2 shows the IV curve for this optical waveguide RTD. Resonance was found to occur at a bias of 0.9 V with a sharp drop in the current indicating bistability but not oscillation. Optical characterisation was carried out with the aim of determining the change in the optical absorption spectrum when the device switched. Optical characterisation of the device employed a Ti:sapphire laser that was tuneable in the wavelength region close to the band-gap resonance of the waveguide, i.e., close to 890 nm. In order to minimise thermal effects in the RTD a pulsed power supply was used. When the pulse amplitude exceeded V_b the current through the RTD would switch rapidly from I_b to I_c (see Fig. 2). An increase in absorption along the length of the RTD was observed upon switching due to the RTD. No change in absorption was observed when the device was biased below V_b.

© 1994 IEEE