512 Sensors and Actuators A, 37-38 (1993) 512-515 Monolithically integrated LED, waveguide and photodetector optical system for near-infrared biosensor P Huertas, G Mler, M L Dotor, J V Angmta, D Golmayo and F Bnones Centro Naczonal de Mzcroelectromca (CSIC), Serrano 144, 28006 Madrrd (Spat) Abstract A novel monohtlucally integrated optoelectronic microsensor 1s fabncated on GaAs substrates by means of a single epltaxlal process step (atonuc layer molecular beam ep~taxy, ALMBE), conventional lithography and selective chermcal etching techniques The nucrosensor integrates an IR (0 86-1 1 pm) lateral ermttmg diode linked through a leaky optical wavegmde to a photo&ode Inlmduction Optical sensors are of cotwderable interest for (blo)chemxal sensing applications In parkular, those which Involve the use of the interaction of an evanes- cent wave with adsorbed species on a waveguide seem pronusmg for blosensors because the penetration depth of an optlcal evanescent wave (typlcally 100 nm) 1sof the same order of magmtude as the thickness of an antlgen- antibody bimolecular complex Several devices using evanescent wave interactions (mterferometnc, plasmon resonance, absorption, etc) have been proposed and developed [l-3] Bnefly, most of them consist of three main components a hght-emlttmg source (generally a laser that must be coupled mto the wavegmde through input optics), a waveglude with an optically leaky area and a photodetector (PD) able to detect the transnutted light (or the fluorescence of the medium m some cases) The intensity of the transmitted hght IS a function of the losses that the evanescent field suffers when propa- gatmg through the sensmg element, which can be a fibre or a planar wavegulde Conventionally these compo- nents are independently fabncated and then mecham- tally assembled We have monohthlcally integrated all these compo- nents m the same chip by epltaxlal growth of a basic diode structure on GaAs substrates This structure IS that of a separated confinement single quantum well (SCHQW) [4, 51 By means of conventlonal hthography and selective chenucal etchmg, the three components (hght emitter, in this case a lateral LED, leaky waveguide and detector) are defined m this SCHQW structure This monohthlc technology 1s very promlsmg because it allows optical sensor structures to be designed for a very large range of wavelengths from vlslble to infrared by choosmg a suitable III-V material combmatlon On 0924-4247/93/$6 00 the other hand, It allows the total device dlmenslons to be reduced to a few hundreds of nucrons In our case the operating wavelength can be selected m the 0 86-l 1 w range by modlfymg the In mono- undopod Fig 1 Structure of quantum-well laser with n = 1 InAs mono- layer m the active regon 9000 - 123156 WVXAYERS hPu lmll Rg 2 Laser enusSion wavelength at room temperature vs InAs monolayer content m the quantum well @ 1993 - Elsev~er Sequoia All nghts reserved