The investigation of structures, defects and electrical properties of GaAs films implanted with arsenic ions

Abstract

The structures, defects and electrical properties in arsenic-ion-implanted GaAs films were investigated. Samples were prepared into two categories, i.e., as implanted films at dosages of 10(12) to 10(16)cm(-2) and the film implanted at the dosage of 10(16)cm(-2) but then post-annealed at Ta = 200-800 degrees C. When using samples implanted at different dosages, the TEM images show a transformation of the structure in the film between 10(13) to 10(14)cm(-2). For the as implanted film at the dosage of 10(13)cm(-2), the structure is polycrystal. But for films at the dosages above 10(14)cm(-2), the structure is amorphous. Due to the transformation of the structure, the lattice expansion (as well as the strain) observed by X-ray reaches to its maximum value in the film at the dosage of 5 x 10(13)cm(-2). Besides, the mechanism of the carrier transport, observed by the temperature dependent conductance, also varies from band conduction to hopping conduction between these two dosages. While the dosage of the implanted and then annealed film was increased above than 10(15)cm(-2), As precipitates are found and many dislocations are accompanied by. As for the implanted and then annealed films, the crystal regrowth phenomena was observed by TEM at temperatures above 400 degrees C. The strain gradually disappear at the same temperature range. The mechanism of the carrier transport also varies from hopping conduction to band conduction at Ta = 300-600 degrees C. As precipitates and the dominant point defects of Ga-As and V-As in the film are found while Ta was around 500 degrees C. Furthermore, from the investigation in X-ray photoelectron spectroscopy we measured the binding energies and barrier heights(phi(bh)) of Schottky diodes in films, a model of effective barrier height is obtained to explain the electrical properties of carrier transport in implanted S. I. GaAs films and the implanted N+ GaAs films. In addition, while Ta was increased above 600 degrees C, the properties in the film show different from those at Ta lower than 600 degrees C. Point defect of V-Ga becomes dominant in the film due to its larger diffusion constant via the temperature. The amount of this and dosage of 10(12) - 10(16) cm(-2), respectively. Some of the As+-implanted GaAs were annealed in the nitrogen ambient with GaAs caps at the temperature of 200 degrees C to 800 degrees C for 30 minutes. Before deposition metal on the film for making Schottky diodes, surface oxide was removed by etching solution of HCl (HCl : H(2)0 = 1 : 1). Diodes were made on the implanted S.I. and N+ GaAs samples with gold as Schottky contact under the condition of low vacuum pressure similar to 10(-6) torr. For temperature-dependent conductance measurements, two Ohmic contacts with gap of 35 micron were deposited on the implanted S.I. GaAs samples.