Hall electron concentration as a function of temperature (80: ST~ 300 K) has been measured
on samples of Gal _ x Alx As with compositions x in the range 0.23~ x~ 0.32. The
measurements are repeated for the same crystals and for various constant hydrostatic
pressures to alter their band structure. The results show that a deep level is present in the
crystals whose activation energy initially increases with pressure, being 5 and 145 meV for
P= 0 and 20 kbars, respectively, for x= 0.23. For P> 20 kbars, the activation energy …