We present a correlation between the behaviour of the RHEED specular reflected beam intensity during the initial phases of growth, the MBE growth conditions (T(s), P(As4), V(GaAs)), and the surface morphology examined by Nomarski contrast microscopy after the growth of a 2-mu-m GaAs layer on (001) GaAs substrates. The quality of the layers was also checked by low-temperature photoluminescence. We found that the steady-state intensity of the reflected beam gives a direct indication of the smoothness of the growth surface. From the RHEED pattern comparison we obtained: (i) for a fixed growth temperature and V/III beam equivalent pressure (BEP) ratio, a lower growth rate leads to smoother surfaces; (ii) at a fixed growth temperature and growth rate, there is an optimum As4 pressure which gives the maximum number of oscillations that can be observed before reaching a steady-state intensity. This optimum As4 pressure induces a minimum surface roughness and a high low-temperature photoluminescence (PL) intensity. Low-temperature photoluminescence measurements showed that the growth at 585-degrees-C instead of 620-degrees-C or at greater BEP V/III ratio, leads to higher incorporation of shallow impurities.