University of Essex Nanofab

These pages provide an overview of the semiconductor device research and teaching nanofabrication facilities

Wet Chemical Etching

Selective Etchants for AlGaAs/GaAs Structures 

1)     HCl (conc.) etches AlGaAs when Al >= 60% but does not etch GaAs only removes the oxides of GaAs

2)     Ammonium hydroxide: Hydrogen Peroxide ratio1:19

        etch rate 10um/min Etches GaAs but not AlGaAs for Al% > 30%. A reliable etch stop is 100nm of AlGaAs where Al>50%

3)     Citric Acid: Hydrogen Peroxide ratio 10:1

        etch rate = 0.2um/min

        Selectivity for etching GaAs (roughly 100:1) over AlGaAs when Al = 30%

        Citric acid:di water = 1:2 weight (gms) to volume (ml) ratio

        J.Vac.Sci.Tech B8 1122 (1990), C.Juang et al

One useful etch for GaAs based structures has the ratio sulphuric acid:hydrogen peroxide:deionised water = 1:8:80

It has an etch rate of about 0.5 microns per minute in undoped GaAs; and has the particular virtue that the etched surface is flat at the base of the mesa.

J.Electrochem.Soc. 128 p874 (1981), D.W.Shaw