  The parameters of two-dimensional electron gas (2DEG) in a GaAs/AlGaAs
heterostructure were determined by an acoustical (contactless) method in the
delocalized electrons region ($B\le$2.5T). Nonlinear effects in Surface
Acoustic Wave (SAW) absorption by 2DEG are determined by the electron heating
in the electric field of SAW, which may be described in terms of electron
temperature $T_e$. The energy relaxation time $\tau_{\epsilon}$ is determined
by the scattering at piezoelectric potential of acoustic phonons with strong
screening. At different SAW frequencies the heating depends on the relationship
between $\omega\tau_{\epsilon}$ and 1 and is determined either by the
instantaneously changing wave field ($\omega\tau_{\epsilon}$$<1$), or by the
average wave power ($\omega\tau_{\epsilon}$$>1$).
