Microwave induced resistance and photovoltage oscillations were investigated in MgxZn1-xO/ZnO heterostructures. The physics of these oscillations is controlled significantly by scattering mechanisms, and therefore these experiments were motivated by the recently achieved high quality levels in this material and the apparent dominance of large angle, short-range scattering, which is distinct from the prevailing small angle scattering in state-of-the-art GaAs structures. Within the studied frequency range of 35-120 GHz, up to four oscillations were resolved at 1.4 K temperature, but only in high density samples. This allowed us to extract the value of the effective electron mass m* = (0.35 +/- 0.01)m(0), which is enhanced over the bare band mass, and estimate a local quantum scattering time of about 5 ps.