The stability of the electrical isolation in n-type GaAs layers irradiated with ions of different mass is compared. The irradiations were performed with proper doses of 1 H ϩ , 4 He ϩ , or 11 B ϩ ions to create specific damage concentration level which lead to: ͑i͒ the trapping of practically all the carriers ͑R s Ϸ10 8 ⍀/ᮀ), ͑ii͒ the onset of hopping conduction ͑R s Ϸ10 8 ⍀/ᮀ), and ͑iii͒ a significant hopping conduction ͑R s Ϸ10 6 ⍀/ᮀ). Irrespectively of the ion mass, the temperature range for which the isolation is preserved, i.e., R s Ͼ10 8 ⍀/ᮀ, extends up to 200 or Ϸ 600°C, respectively, for the cases ͑i͒ and ͑ii͒. In case ͑iii͒, this range comprises temperatures from Ϸ 400 to 650°C. Annealing stages at 200 and 400°C recover in a great extent the conductivity and improve the carrier mobility in low dose irradiated samples ͓case ͑i͔͒. In samples irradiated to higher doses ͓cases ͑ii͒ and ͑iii͔͒, the conductivity recovers in a single stage.

The evolution of the sheet resistance (Rs) in n-type GaAs layers during ion irradiation was studied using light mass projectiles like proton, deuterium, and helium ions at various energies. For all the cases, at the beginning of the irradiation, Rs increases with the accumulation of the dose. After reaching ≊109 Ω/⧠, Rs saturates, forming a plateau. This plateau is succeeded by a decreasing of Rs with the increase of the dose, denoting that conduction via damage-related mechanisms is taking place. The threshold dose to convert the conductive layer to a highly resistive one at room temperature or at 100 °C is found to scale with the inverse of the estimated number of displaced lattice atoms along the depth of the doped layer. Antisite defects formed by the replacement collisions are invoked to play the major role in isolation formation in GaAs by virtue of their lower sensitivity to dynamic annealing compared to other point defects.

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Ferromagnetic clusters were incorporated into GaAs samples by Mn implantation and subsequent annealing. The composition and structural properties of the Mn-based nanoclusters formed at the surface and buried into the GaAs sample were analyzed by x-ray and microscopic techniques. Our measurements indicate the presence of buried MnAs nanoclusters with a structural phase transition around 40 °C, in accord with the first-order magneto-structural phase transition of bulk MnAs. We discuss the structural behavior of these nanoclusters during their formation and phase transition, which is an important point for technological applications.

The electrical isolation in n-type GaAs layers produced by proton irradiation at temperatures from −100 to 300 °C was investigated. The threshold dose for the isolation (Dth) was found almost identical for irradiation at temperatures from −100 to 220 °C. At 300 °C, a dose of ≅1.3 times higher is required for the isolation threshold. In samples irradiated to a dose of Dth at −100 °C or nominal room temperature, the isolation is maintained up to a temperature of ≈250 °C. In those samples irradiated at 300 °C it persists up to ≈350 °C. For doses of 3Dth or above, the stability of the isolation is limited to temperatures of 450–650 °C, irrespective of the irradiation temperature (Ti). For practical applications where doses in excess to 5Dth are usually employed, the irradiation temperature (from −100 to 300 °C) has only a minor effect on the formation and thermal stability of the electrical isolation.