This paper reports initial characterisation results for planar mid-wavelength infrared (MWIR) photodiodes fabricated using a novel reactive ion plasma-induced n-on-p junction formation technology on vacancy-doped p-type HgCdTe grown by LPE on CdZnTe substrates. The junction is formed without the need for post-implant annealing typically required by ion implantation junction formation techniques to repair damage or to move the junction away from damaged regions. The dark current and dynamic resistance, R-d, of the fabricated photodiodes have been characterised as a function of temperature. At 80 K, the zero-bias dynamic resistance-junction area product (R(o)A) of the diodes is 4.6 x 10(7) Ohm cm(2), with the devices being diffusion limited down to similar to 135 K. Dynamic resistance has been measured for temperatures between 80 and 195 K and biases between - 200 and + 150 mV. Modelling of the observed dark current has been undertaken using three distinct mechanisms, diffusion, generation-recombination, and tray-assisted tunnelling. The results show that the plasma-induced junction formation technique can produce high-performance planar HgCdTe photodiodes. The dark current mechanisms found in these devices are similar to those found in diodes formed using conventional ion implantation techniques.