A WET ETCHING TECHNIQUE FOR ACCURATE ETCHING OF GAAS ALAS DISTRIBUTEDBRAGG REFLECTORS/

We have demonstrated a wet etching technique capable of producing accu rate and uniform etch depths in distributed Bragg reflectors (DBRs) an d other GaAs/AlAs superlattice structures. The process utilizes two se lective etchants, citric acid/hydrogen peroxide in a 4:1 ratio and pho sphoric acid/hydrogen peroxide/water in a 3:1:50 ratio, to sequentiall y etch away each pair of superlattice layers. We have used this techni que to expose a 680 Angstrom thick conducting GaAs layer buried beneat h a 15 period, 2.1 mu m thick; undoped GaAs/AlAs DBR mirror. Transmiss ion Line measurements pads were formed on the exposed layer to determi ne the contact and sheet resistance. Comparison with a similar layer o n the surf ace of the wafer reveals that the exposed layer is easily c ontacted with only a slight increase in sheet resistance indicating le ss than 125 Angstrom of overetching, 0.6% of the total etch depth.