Excitonic recombination processes in GaAs grown by close-space vapour transport

https://doi.org/10.1016/j.mejo.2004.03.002Get rights and content

Abstract

Epitaxial GaAs layers were grown using the close-space vapour transport. From deep level transient spectroscopy measurements, the native EL2 donor has been observed in all of the layers with deposition temperature-dependent concentration. On the GaAs samples, also performed are photoluminescence experiments in the temperature range 10–300 K. Two peculiar features were revealed: (i) the radiative recombination in GaAs layers is increasingly dominated by bound–exciton transitions, (ii) the excitonic luminescence is found to be very sensitive to the growth conditions. A study of the near-band-edge photoluminescence as a function of power excitation and temperature has been done in an attempt to elucidate the origin of the enhanced bound–exciton luminescence.

Introduction

The growth of epitaxial layers in III-V semiconductors by close-space vapour transport (CSVT) has been paid recently a great deal of interest for both fundamental and applied physics. The CSVT technique is characterised by a close spacing between source and substrate. This arrangement in space provides a large mass transfer during the decomposition and the recomposition reactions. Additionally, the rate of transport can be easily controlled by monitoring both the source and substrate temperatures and the water vapour pressure. Epitaxial GaAs layers of high crystalline quality and having a reasonable electron mobility have been realised using CSVT [1]. Electrical and optical properties of CSVT deposited GaAs have been investigated [2], [3], [4]. To judge the interest of this material, it is required to know in more detail the effects of the growth conditions on the characteristics of deposited layers. On the other hand, it was evidenced from thermodynamical considerations that the CSVT GaAs is As-rich [5]. This property can favour the formation of the EL2 centre in these layers [6], [7]. Indeed, standard deep level transient spectroscopy (DLTS) measurements have shown unambiguously the existence of the EL2 level in all of the CSVT samples studied [4]. The assignment of this deep donor is also supported by optical quenching [8]. It is worth to notice that the occurrence of deep acceptor states related to possible gallium vacancies (VGa) has been invoked as well in materials grown by CSVT, based on experimental and theoretical investigations [9], [10], [11], [12], [13].

This paper reports on a DLTS and photoluminescence (PL) study of CSVT deposited GaAs layers. The deep EL2 donor has been observed with substrate temperature-dependent concentration. From PL measurements, the bound–exciton (B–E) recombination was revealed to be dominant at low temperature. It was also found that the B–E PL intensity increases with the substrate temperature. An attempt to assign the latter behaviour to increased concentration of impurities and/or stoichiometric defects that bind the excitons will be presented.

Section snippets

Results and discussion

The epitaxial set-up used for this investigation consists of CSVT deposited GaAs layers. The samples are undoped. The source and substrate are both a high-purity (001) oriented GaAs. The substrate temperature (θ) was varied in the range 750–800 °C. A nominal temperature difference of 50 °C has been established between source and substrate. The water vapour pressure is fixed at 1.25 mm Hg during the growth. The DLTS measurements were performed in the temperature range 77–450 K using a double

Conclusion

Epitaxial GaAs layers were grown by CSVT under different growth conditions. They have been investigated using DLTS and PL. The native EL2 donor is consistently observed in all of the layers. It was found that the concentration of this centre increases with the substrate temperature. The PL study led to two main observations: (i) the NBE luminescence is increasingly dominated by B–E transitions at low temperature, (ii) the efficiency of the B–E luminescence increases with the substrate

References (18)

  • J. Mimila-Arroyo et al.

    Proceedings of the 16th IEEE Photovoltaı̈c Specialists Conference

    (1983)
  • J. Mimila-Arroyo et al.

    Solid State Commun.

    (1984)
  • J. Mimila-Arroyo et al.

    J. Appl. Phys.

    (1985)
  • B.A. Lambos et al.

    J. Appl. Phys.

    (1990)
  • D. Coté et al.

    J. Electrochem. Soc.

    (1986)
  • M.D. Miller et al.

    Appl. Phys. Lett.

    (1977)
  • J. Lagowski et al.

    Appl. Phys. Lett.

    (1982)
  • G. Vincent et al.

    J. Appl. Phys.

    (1982)
  • E.W. Williams

    Phys. Rev.

    (1968)
There are more references available in the full text version of this article.
View full text