Pressure dependence of the electron effective mass in GaAs up to the 1s(Gamma)-1s(X) crossover

The effect of hydrostatic pressure (P) on the k = 0 conduction band mass m(0)*(P) in lightly Si-doped GaAs is studied by far-infrared magnetospectroscopy. The electron cyclotron resonance (CR) at (T = 17 K), and the 1s-2p(+) absorption of Si donors (at T = 4.2 K), are measured up to 40 kbar under fields of 6 to 9 T by Fourier transform and laser magnetotransmission techniques. DX-center trapping is avoided by visible illumination. A double-bellows diamond-anvil cell and 36 mm bore magnet enable in situ P-B-T tuning. The slopes dE/dB for the CR and 1s-2p(+) peaks decrease with pressure in accordance with effective mass theory, with no sign of strong deepening for the Si Is(T) state. We find m(0)*(P)/m(0)*(a) = 1 + (6.1 +/- 0.3) x 10(-3)P - (1.3 +/- 0.5) x 10(-5)P(2) (P in kbar) from the CR data, after correcting for nonparabolicity via an effective two-band k . p model. This agrees well with prior results limited to 17 kbar, and extends the measurement of m(0)*(P) in GaAs to the Gamma-X crossover.