Defect Induced Luminescence from MBE Prepared Si/Si 1-x Ge x Superlattices
- PDF / 368,605 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 98 Downloads / 257 Views
DEFECT INDUCED LUMINESCENCE FROM MBE PREPARED Si/Si1 1xGex SUPERLATTICESt G.A. Northrop, S.S. Iyer, and D.J. Wolford IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598.
ABSTRACT We report the first definitive observation of photoluminescence from Si/Sil- Ge. superlattice heterostructures. Excitons bound to a deep-level radiation damage center (I,) are observed in a series of low Ge content (x = 0.05) unrelaxed structures. We also present preliminary results on photoluminescence from as-grown narrow period (Si 6Ge4) superlattices. INTRODUCTION Epitaxially grown Si and SilxGe, alloys have received substantial attention in recent years. While considerable success has been achieved in their use in purely electronic devices, such as heterojunction bipolar transistors [1], even the most basic exploration of their optical properties has met with significant difficulties, particularly in the case of optical emission. To date there have been no clearly documented reports of photoluminescence from epitaxially grown Si,.Ge. superlattices. This is particularly troubling in the light of a recent work showing that both intrinsic and dopant bound exciton luminescence are readily observable in bulk grown Si.,,Ge, alloys over the entire alloy range [2]. The only definitive observations of photoluminescence in epitaxially grown single layer alloys have been for recombination at deep levels, particularly through their intentional introduction by radiation damage [3]. In addition to the question of whether epitaxialy grown Si1 ,_Ge. has the luminescence efficiency equivalent to bulk material, is the possibility of radiative recombination rates being significantly enhanced by the careful growth of symmetrically strained narrow period SinGem superlattices. Much theoretical work has concentrated on the possibility that the combination of strain and zone folding in these structures might overcome the indirect gap nature of the two constituents and create optical transitions with large oscillator strengths [4-6]. One report of luminescence between 750 and 850 meV has received considerable attention as possibly being of this nature [7]. This paper will also present results on this system and address the difficulty of establishing the true nature of this type of luminescence. I IN DILUTE ALLOY SUPERLATTICES We have attempted to observe photoluminescence from a number of epitaxially grown layers, including unrelaxed Sil_•Ge. alloy single layers and Si/Si_,,Ge. superlattices, and SinGem symmetrically strained superlattices. All failed to show any feature that could clearly be identified with the epitaxial layers. However, a method for inducing luminescence through the introduction of a deep level, 1,, was quite successful for low Ge content single alloy layers [3]. In the present work we have extended this method to the case of Si/Sio.95 Geo.0 5 superlattices, grown lattice matched to (001) silicon. Three samples, shown schematically in Fig. ), were grown with three different periods to an approximate total thickness of 2200 A,
Data Loading...
