Atomic relocation processes in impurity-free disordered p-GaAs epilayers studied by deep level transient spectroscopy

Abstract

We have used capacitance–voltage and deep level transient spectroscopy techniques to study the relocation of impurities, such as Zn and Cu, in impurity-free disordered (IFD) p-type GaAs. A four-fold increase in the doping concentration is observed after annealing at 925 °C. Two electrically active defects HA (EV+0.39 eV) and HB2 (EV+0.54 eV), which we have attributed to Cu- and Asi/AsGa-related levels, respectively, are observed in the disordered p-GaAs layers. The injection of gallium vacancies causes segregation of Zn dopant atoms and Cu towards the surface of IFD samples. The atomic relocation process is critically assessed in terms of the application of IFD to the band gap engineering of doped GaAs-based heterostructures.

Electrical characterization of p-GaAs epilayers disordered by doped spin-on-glass

“…This suggests that the defect peak at ϳ250 K in the DLTS spectra of disordered samples may consist of the superposition of HC1 and HC2. 21 Following our present understanding of IFD in GaAs, 11,19 we speculate that HC2 may be a defect related to either the As i ͑H3͒ 22 or As Ga ͑HM1͒. 23 One qualification to this tentative assignment is that the double donor state of EL2 ͓i.e., HM1-As Ga ͑+/ + +͔͒ has not previously been observed in epitaxially grown p-GaAs layers.…”

“…23 One qualification to this tentative assignment is that the double donor state of EL2 ͓i.e., HM1-As Ga ͑+/ + +͔͒ has not previously been observed in epitaxially grown p-GaAs layers. We have previously attributed HA and HB1, 19 which are of minor interest here, to defect complexes involving Zn ͑Ref. 20͒ and Cu, 22 respectively.…”

“…1͑b͒ as a function of the inverse of the annealing temperature. The value of ⌬N A corresponds to the difference between N A in a dielectric-capped and annealed sample and N A in the as-grown sample at a depth of 0.4 m. We have previously measured the changes in N A for samples disordered using plasma-enhanced chemical vapor deposited ͑PECVD͒ SiO 2 , 19 and the results ͑solid circles͒ are also shown in Fig. 1͑b͒.…”

“…These plots are not shown here because they are identical to those we have reported previously. 19 We also compared the signatures of IFDinduced defects in p-GaAs with those reported in the literature in order to allow their tentative identification. The asgrown layers contained the defects commonly observed in MOCVD-grown p-GaAs: HB2 ͑E T ϳ E V + 0.39 eV; a ϳ 6.3 ϫ 10 −15 cm 2 ͒ and HC1 ͑E T ϳ E V + 0.57 eV; a ϳ 3.0 ϫ 10 −15 cm 2 ͒, in concentrations ϳ2 ϫ 10 12 and ϳ4 ϫ 10 12 cm −3 , respectively.…”

“…As mentioned earlier, we have previously attributed HB2 to the Cu-related acceptor level in p-GaAs, but without providing much evidence for the assignment. 19 Before discussing the effect of annealing temperature on the creation of this prominent defect in disordered p-GaAs, we discuss the electrical and optical properties of HB2 in more detail. It is well established that Cu introduces two acceptor levels at E V + ͑0.13-0.15͒ eV and E V + ͑0.40-0.49͒ eV in the band gap of GaAs, albeit the exact structure of these levels are not known.…”