• PDF / 208,989 Bytes
• 5 Pages / 420.48 x 639 pts Page_size
• 51 Downloads / 227 Views

DOWNLOAD

REPORT

---

PHOTOLUMINESCENCE EXCITATION SPECTROSCOPY OF MOCVD-GROWN: GaAs:V Y.J. KAO, AND N.M. HAEGEL Dept of Materials Science and Engineering, University of California - Los Angeles, Los Angeles, CA 90024; W.S. HOBSON, AT&T Bell Laboratories, Murray Hill, NJ 07974.

ABSTRACT Photoluminescence excitation spectra have been obtained at 4.2 K for the characteristic V3 + intracenter emission (0.65 - 0.75 eV) of MOCVD-grown GaAs:V. Oscillatory structure of the PLE spectrum with above-band-edge excitation has been observed in GaAs:V for the first time. The oscillatory period is found to be 41.3 ± 0.5 meV, corresponding to [1 + (m*,/mhh)]thWLO, and is due to energy relaxation of conduction band electrons through LO phonon emission. Our results suggest capture by a shallow donor as an intermediate step in the luminescence from the V center.

INTRODUCTION Vanadium is a substitutional impurity in GaAs which is known to have a characteristic crystal-field luminescence band in the 0.65 - 0.75 eV energy range [1]. It has been shown that vanadium gives rise to a deep acceptor level at Ec - 0.15 eV [2,3,4]. Figure 1 shows the substitutional vanadium levels in GaAs [4]. In this study, photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies have 3 been used to study the characteristic V + emissions of MOCVD-grown GaAs:V. One of the results that emerged from this study is that an oscillatory structure in the PLE spectrum with above-band-edge excitation has been observed.

EXPERIMENTAL A barrel-type OMVPE reactor operated at atmospheric pressure was used for all the GaAs growth runs. Trimethylgallium (TMG) and arsine (AsHa) were employed as the source chemicals with a V/Ill ratio of 15. Both H2 and He carrier gases were used with qualitatively similar results. The typical growth rate and temperature were 3.7 pm/h and 675°C, respectively. The ultra-high-purity VO(OC2 H5) 3 source was held at 10'C in a thermostatic bath. The detailed processes of the growth and chemical analysis were described in a previous report [5]. Some of the samples were additionally doped with Si and/or Be in order to systematically vary the Fermi levels in the epitaxial layer and change the charge state of the vanadium. In the PL measurements, samples were immersed in liquid He and excited with an Ar ion laser at A = 514.5 nm. The luminescence was detected using a cooled PbS detector. The spectra were calibrated for the spectral response of the system with a blackbody source. In the PLE measurements, the excitation source was replaced by a combination of a 75 W tungsten lamp and a 0.25 m grating monochromator. The output intensity of the excitation source was normalized for constant lamp intensity. The 0.65 - 0.75 eV luminescence band was selected by using a 1.6 pm long-pass filter or a monochromator.

RESULTS AND DISCUSSION All of the n-type and semi-insulating (SI) vanadium-doped GaAs exhibited the same infrared PL band centered at 0.65 - 0.75 eV, although the ratio of band edge of deep level PL intensity varied. A typical PL spectrum from these sa