Strong Stark Effect in Electroluminescence from Phosphorous-Doped SOI-MOSFETs


Jin-ichiro Noborisaka, Katsuhiko Nishiguchi, Yukinori Ono, Hiroyuki Kageshima, and Akira Fujiwara
Physical Science Laboratory

 The electronic states of phosphorous atoms in silicon (Si) are now attracting much attention because they could be useful for solid-state quantum computers. We report a strong Stark effect in electroluminescence (EL) from phosphorous-doped silicon-on-insulator (SOI)-MOSFETs when electrons are injected into the sub-10-nm-thick SOI channel by tunneling [1].
 The devices were SOI-MOSFETs with an n-type polycrystalline Si (poly-Si) tunneling gate [Fig. 1(a)]. Two SOI thicknesses (tSOI) of 8.5 and 25 nm were prepared. The thicknesses of the front-gate oxide (FOX), and the buried oxide (BOX) were approximately 2 and 400 nm, respectively. The potential profiles for the device are shown in Fig. 1(b). Due to the thermal treatment for the device fabrication, the SOI channel was phosphorous-doped on the order of 1017 cm-3. Electroluminescence spectra were taken at temperature (T ) of 80 K. Electrons are injected from the front gate into the SOI channel, while holes are injected from the boron doped p+ contact. Figure 2(a) shows the VBG dependence of the EL spectrum for the device with tSOI of 25 nm. The EL intensity decreased as VBG was positively increased, producing an electric field in the SOI so that electrons distribute near BOX/SOI interface. Then electrons and holes are strongly separated, which results in the decrease of the EL intensity. On the other hand, the VBG dependence of the EL spectra for tSOI of 8.5 nm showed complicated behavior [Fig. 2(b)]. The peak for a neutralized donor and free-hole recombination (D0-h) showed Stark shift of up to 50 meV at VBG of 136 V. The EL intensity kept a higher value even when that for 25 nm became almost zero, and then suddenly decreased around VBG of 80 V [Fig. 2(c)]. The sudden change of the EL intensity can be explained by electron dissociation from strongly bound states. In contrast to the thicker QW, the ground state of triangular well at the BOX interface in the QW for tSOI of 8.5 nm is higher than that of phosphorous-bound state at low electric field. Therefore, electrons bound at phosphorous atoms hardly dissociate in the thin QW. This is the reason for the difference in the specific field needed to cause the sudden decrease of the EL intensity.

[1] J. Noborisaka et al., Appl. Phys. Lett. 98 (2011) 033503.

Fig. 1. (a) Schematic cross section of the device structure (top) and
top view of the device (bottom). (b) Potential profile from
source to drain (top) and from top to bottom of the device
Fig. 2. (a) The VBG dependence of EL for tSOI = 25 nm. (b) That for tSOI = 8.5 nm.
The arrows trace the peak for D0-h. The voltage steps for VBG are 10 V
except for |VBG| of 136 V. (c) The VBG dependence of the integrated EL

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