Wafer Bonding: Light Emitters

Abstract

Abstract People Publications Projects Alumni

M. Reiche and T. Wilhelm

Light emitting diodes (LED) fabricated by either boron [1] or phosphorus [2] implantation into Si attract special interest. They allow efficient room temperature (RT) electro-luminescence (EL) of the Si band-to-band (BB) line at 1.1 μm. The BB luminescence is an intrinsic property of Si. The radiative BB transition is assisted by a TO phonon yielding an energy of the BB light EBB = EG - ETO. Light emitters fabricated on defect-free silicon show the BB line at about 1.1 μm only (Fig. 1). The efficiency of the BB emission depends on ratio of the radiative BB recombination rate to the total recombination rate.

Dislocations in Si represent a competing recombination channel and form the quartet of D lines appearing at larger wavelength (Fig. 2).  The application of dislocations as active parts of LEDs requires to reproducible formation of their structure and position, respectively. Si wafer direct bonding is suitable to form a regular dislocation network. The structure of a dislocation network, i.e., density and type of the dislocations formed, depends on the misorientation angles for tilt and twist during wafer bonding. The dislocation network can be well reproduced by adjusting the angles. Fig. 3 demonstrates that luminescence spectra are strongly dependent on the structure of the dislocation network. Hence, the luminescence spectrum can be tailored by the misorientation angles in a controlled manner and dominance of either D1 or D3 radiation may be obtained. A layer transfer treatment allows to position the dislocation network close to the wafer surface. The network can be fabricated at depths from  less than 50 nm to micrometers below the surface. Network structures that generate only D1 line luminescence could be produced by dislocation engineering, see [3].

Fig. 1: Electroluminescence spectra obtained on n+p- and p+n-junctions produced by ion implantation of phosphorous (135 keV, 1∙10¹⁴ at/cm²) and boron (50 keV, 1∙10¹⁴ at/cm²), resp. Measurements at room temperature.

Fig. 2: Photoluminescence spectrum of dislocated silicon showing D1-D4 dislocation lines and band-band line.

Fig. 3: Luminescence spectra (T = 80 K) obtained for dislocation networks with different misorientation angles. A: twist angle of 9°, broad emission with maximum at D1 line; B: twist angle of 8.2°, maximum at D3 line, same tilt angle of 0.2° for both A and B; C: tailored network with clear dominance of D1 line [3].

[1] W.L. Ng, M.A. Lourenco, R.M. Gwilliam, S. Ledain, G. Shao, K.P. Homewood, Nature 410, 192 (2001).
[2]. M. Kittler, T. Arguirov, A. Fischer, W. Seifert, Optical Materials 27, 967 (2005).
[3] M. Kittler, M. Reiche, T. Arguirov, W. Seifert, X. Yu, IEDM Tech. Digest 2005, 1027 (2005).