Pressure study of metastability inGa1−xA1xAsGaAs:Siheterojunctions

Abstract

The variation of two-dimensional electron concentration $n_s$ with temperature was studied in $\mathrm{Ga}\frac{\mathrm{As}}{{\mathrm{Ga}}_{1-x}}{\mathrm{A}1\mathrm{}}_x\mathrm{As}\mathrm{}(x=0.3,0.35\mathrm{})\mathrm{}$ heterojunctions under true hydrostatic (gaseous helium) pressure. The metastable behavior of the sample, resulting from the large-lattice relaxation character of the Si donor is clearly seen below 120 K. The effects are reversible above $T_k=160\mathrm{}$ K. The metastable character of the Si impurity makes it possible to lower the concentration by as much as tenfold at zero pressure. By appropriate gas-pressure cycling, any intermediate value of electron density is also obtainable. Using the gaseous medium we were able to vary the pressure at low temperatures, when the sample was in a metastable state. The most significant result obtained using this technique is that the concentration in this metastable state does not vary with pressure. We show that this is closely connected with the pressure independence of the band-gap offset $\Delta E_c$.