On-chip ATR sensor ($\lambda$ = 3.4 $\mu$m) based on InAsSbP/InAs double heterostructure for the determination of ethanol concentration in aqueous solutions

We discuss photoelectrical properties of an on-chip attenuated total reflection (ATR) sensor for the ethanol concentration measurements in an aqueous solution. The on-chip sensor/microchip was made from a $p$-InAsSbP/$n$-InAs monolithic double heterostructure with three mesas/individual diodes grown on a single $n^+$-InAs substrate/waveguide. Two heterostructure diodes were used as photodiodes, while the third one – as a LED. The ethanol concentration was measured via an algorithm based on analysis of the I–V characteristic parameters of a photodiode and the L–I characteristics of the LED.