Ultrafast ion-implanted InGaAs metal-semiconductor-metal photodetectors

Abstract

Metal-semiconductor-metal photodetectors with interdigital electrode pattern are very attractive for applications in ultrafast optoelectronics and electronics such as high-speed switching and signal processing. In order to extend their bandwidth beyond the transit-time limit, ultrafast III-V semiconductor materials such as low-temperature grown GaAs [ 13 or highly Er-doped M a [2]with picosecond carrier lifetimes have been employed. For ultrafast long-wavelength applications, which have gained particular importance since the emergence of Er-doped fiber amplifiers, InGaAs grown lattice-matched to InP is the material of choice. In this case, however, the procedure of low-temperature growth could not be successhlly implemented thus far to fabricate practically u s e l l ultrafast MSM photodetectors because the resulting material resistivity is fairly pow [3]. An alternative method is ion-implantation. It has been applied previously for obtaining very short carrier recombination lifetimes in photoconductive switches [4]. Here, we shall demonstrate the great potential of ion-implantation for improving the bandwidth of InGaAs MSM photodetectors. The epitaxial layer sequence of the devices under study is grown by LP-MOCVD on semiinsulating InP substrates. It consists of an InP:Fe buffer layer, an 0.7 pm thick InGaAs:Fe absorption layer, and an 30 nm thin InP:Fe cap layer for enhancing the Schottky barrier height. Electron-beam evaporated Pt/Ti/Pt/Au Schottky contacts with interdigitated electrode fingers of 1 pm separation and 0.8 pm width are formed by photolithography. The photoactive area is 18 pm square. The devices are connected to coplanar waveguide transmission lines which have a nominal impedance of 50 Q. Fabricated devices are implanted with nitrogen ions under conditions thiit will be described in detail elsewhere. The device characteristics prior and after implantation are measured ,,on-wafer" under top-side illumination. The dark current (at 6.5 V bias) is observed to increase from typically 100 nA to about 10 pA as a consequence of implantation. The cw-quantum yield at 1.55 pm wavelength decreases fi-om about 25% to 0.25% indicating that the caiiier lifetime is drastically reduced through the implantation. High-frequency circuit properties are assessed by measurement of the SI]-parameter in the range fiom 50 MHz to 40 GHz. S I ] is obseived to remain unaffected by the ion-bombardment. Moreover, it is independent of the applied bias voltage. Fitting of the data to a

Travelling-wave photonic mixers for increased continuous-wave power beyond 1 THz

“…Suggested materials not used yet Ion-impl. InGaAs [23] centre of charge is drifting only relatively slowly into the direction of the E-field. For this complicated situation, no explicit equations are available (1/τ = 1/τ rec + 1/τ trans is just wrong for our case), while some numerical results have been obtained by Monte Carlo simulations [16].…”