The I-V characteristics of AlGaInP/GaInP bulk and multiquantum barrier n-i-n diodes between 20 and 300 K were measured with pA current resolution. When analysed using a thermionic emission model, measured activation energies in the bulk structures were close to the expected conduction band offset. The interplay of other transport mechanisms, including Fowler-Nordheim tunneling and Poole-Frenkel emission was investigated in both the bulk and multiquantum barrier diodes. Transition points between different regimes were observed. Similarities and differences were observed for the bulk and multiquantum barrier diodes. Measured Fowler-Nordheim barrier heights in the bulk barrier diodes agree well with those derived from simulations except in the case of the indirect material at forward bias.