EN
The E_{c}-0.22 eV trap in Horizontal Bridgman undoped n-type GaAs may be passivated by contact with phosphoric acid for 8 hours at room temperature. Isochronal annealing, at around 250°C for 1 hour resulted in the partial recovery of this defect. The possible mechanisms of E_{c}-0.22 eV trap passivation are proposed.