The evolution with time of the leakage current in mercuric iodide devices has been investigated. It is shown that this evolution can be closely associated with the accumulation of an electric charge which modifies the electric field in the bulk. Under particular biasing conditions, release of this charge leads to the rise of a current peak after a time delay which depends on the experimental parameters. The evolution of this peak has been investigated as a function of injected charge, voltage and temperature. As this phenomenon can be correlated with the short time behaviour of the devices, it can be used to characterize the materials devoted to the preparation of devices such as nuclear radiation detectors.