Passivation of a Bulk Defect E_c-0.22 eV in GaAs by Contact with Phosphoric Acid

Abstract

The Εc-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. Τhe possible mechanisms of Εc-0.22 eV trap passivation are proposed.PACS numbers: 71.55. Eq, 81.60.Cp, 61.70.At The electronic properties of GaAs depend critically on the localized levels in the forbidden gap. The technological procedures during semiconductor device processing often involve the contact of chemicals like acids or solvents with the semiconductor surface. It has been noticed only recently that these treatments are not as benign as they had been thought and they are capable to change the semiconductor properties [1]. It is our aim to report on the changes of defect concentration in bulk GaAs detected by DLTS (Deep Level Transient Spectroscopy) when GaAs is in contact with phosphoric acid in ambient temperature. We propose that these changes are due to hydrogen diffusion into the near-surface region of the samples. The source of hydrogen is the acid itself.Τhe material examined was undoped (n = 1.5x 10ί 5 cm-3) Horizontal Bridgman GaAs grown in MIT (USA). Two sets of samples were prepared. The samples from the first set were measured and then immersed in 60 % H3PO4 at room temperature for 8 h. Afterwards they were annealed isochronally for 1h between 200° C and 300° C in vacuum (5 x 10' 5 Torr). The samples were heated from room temperature to final annealing temperature in 5 mi. The samples from the second set were subjected to electrolysis in 60 % H3 Ρ O4 at room temperature for 8h. They served as a cathode of electrochemical cell with Pt foil as an anode. Τhe current density was 1 A/cm2 . The DLTS spectrum of as-grown material revealed 4 peaks *This work was supported in part by CPBP 01.05.(277)