NEAR AND MID INFRARED SILICON GERMANIUM BASED PHOTODETECTION/

Short-period silicon/germanium (SimGen) superlattice and SiGe quantum well (QW) structures have been grown by molecular beam epitaxy (MBE) o n (100)Si substrates for near (1.3 mu m) and mid-infrared (3-5 mu m; 8 -12 mu m) detection. For the near IR detection - suitable for fibre op tical communication within a Si integrated circuit (IC) chip - short-p eriod Si1-xGex superlattices with period lengths of several atomic mon olayers (ML; e.g. m = n = 5 ML; 1 ML-1.4 Angstrom) and 2-4 monolayers wide p-doped Ge quantum well layers separated by 20 MLs of Si and embe dded in two 10-nm thick Si1-xGex layers have been grown. In the superl attice structure the zone folding effect (U. Gnutzmann, K. Clausecker, Appl. Phys. 3 (1974) 9) has been predicted to produce strong interban d transitions near 0.8 eV (approximate to 1.3 mu m), in the latter one the sharp Si/Ge hetero-interfaces break the k-selection rules and str ong localisation of electron and hole wave function favour a strong in terband excitonic transition at 1.3 pm. This results in a rather effic ient room temperature photo- and electroluminescence and in sufficient absorption. An integrated waveguide/photodetector deposited on a SIMO X (Si substrate with separation by implantation of oxygen) substrate h as been fabricated and an external quantum efficiency of 11% with an i mpulse response time of 400 ps has been observed. For the mid IR range (3-5 mu m) highly p-doped Si/SiGe quantum well detectors have been de posited on an undoped, double-sided polished Si substrate based an het ero-internal photoemission (HIP) over the Si/SiGe barrier. The absorpt ion and photocurrent spectra have been measured from fabricated mesa d etectors at 77 K. The photoresponse spectrum of the HIP detectors is s hown to be widely tunable in the technological important wavelength ba nd 3-5 pm by choice of Ge-content, well thickness and doping level. Qu antum efficiencies of similar to 1% at 4 mu m and 77 K have been achie ved from SiGe HIP structures, dark currents as low as 10(-8) A/cm(2) c an be obtained by modulation doping. Detectivity values of D of 10(9) cm root Hz/W have been achieved, the quantum efficiency spectrum is c onsiderably broader and up to a factor of 4 higher than Pt:Si at 4 pm. (C) 1998 Published by Elsevier Science S.A. All rights reserved.