K. Bacher et Js. Harris, A WET ETCHING TECHNIQUE FOR ACCURATE ETCHING OF GAAS ALAS DISTRIBUTEDBRAGG REFLECTORS/, Journal of the Electrochemical Society, 142(7), 1995, pp. 2386-2388
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.