Spatial extent of band bending in diamond due to ion impact as measured by secondary electron emission: Experiment and theory

Although hydrogentated diamond emits exceptionally high numbers of electrons upon single ion impact, the secondary electron yield decays at an extremely rapid rate as a function of ion fluence. We report measurements of this rapid decay at extremely low fluences where the ion tracks are widely separated and explain the results by a model based on the downwards bending of the conduction band edge, due to positive charge trapped within the ion track. The present work demonstrates the importance of charge trapping in explaining the electronic properties of diamond and other wide band gap materials.

Figure 1

(Color online) Normalized secondary electron emission coefficient, $\delta$, measured with electron probe beams in the energy range $1–30\mathrm{keV}$, as a function of $30\mathrm{keV}$ Ga ion fluence. The solid lines represent fits to the data for the slow decay regime.

Figure 2

(Color online) The low fluence portion of the data of Fig. 1 plotted on an expanded scale showing the normalized secondary electron emission coefficient, $\delta$, measured with electron probe beams in the energy range $1–30\mathrm{keV}$, as a function of $30\mathrm{keV}$ Ga ion fluence. The solid lines represent fits to the data for the fast decay regime.

Figure 3

The effective radius of the region around each ion impact point from which secondary electron emission is suppressed, as a function of the probing electron energy. The radii from the slow decay (triangles) are independent of probing electron energy, whereas the radii (squares) from the fast process increase from $9\text{to}19\mathrm{nm}$ with increasing probing electron energy. The dashed line represents the results of the numerical model for the fast regime for a background hole concentration of $1.5\times {10}^{17}\text{holes}∕{\mathrm{cm}}^3$.

Figure 4

(Color online) The width of the band bending at $1\mathrm{eV}$ below the conduction band edge as a function of the acceptor doping concentration as obtained from the simulations. The inset shows the effect of trapped charge on the conduction band structure as a function of distance from the core of the ion track for different values of acceptor doping concentration as obtained from the TCAD (see Ref. 8) simulations. Note that the distortion of the band structure can extend as much as $80\mathrm{nm}$ from the core of the ion track (the size of which is shown by the bar in the inset) for the parameters modeled here.