Quantized carriers in a small world

In very thin films, or in very thin semiconductor inversion layers, electrons are quantized in the thin potential well, but can move freely in the lateral directions of the film. The resulting band structure is multiple parabolic curves called subbands (orange curves in the figure below).

We have been developed a method to directly measure the valence subband dispersions using Angle-Resolved Photoelectron Spectroscopy (ARPES). Applying this method, we have measured subband dispersions in various semiconductor inversion layers.   

Current research topic:

1. Mechanism of Quantization of Bloch electrons in 2D

2. Development of novel method to evaluate active dopant concentration in sub-surface region.

3. Search of actual band bending potential of p-type space charge layer.

[references]

1. S. N. Takeda, N. Higashi, H. Daimon, "Visualization of In-Plane Dispersion of Hole Subbands  by Photoelectron Spectroscopy"Phys. Rev. Lett. 94, 037401 (2005)　   

Now, we can observe valence subband dispersion!  

2. M. Morita, S.N. Takeda, M. Yoshikawa, A. Kuwako, Y. Kato, H. Daimon,  "ARPES measurements on Si(111) hole subband induced by Pb and Ga adsorption",   Appl. Surf. Sci.,254, 7872 (2008)   

We could see the valence subbands dispersion in the other surfaces.

3. Y. Tanigawa, S. N. Takeda, M. Morita, T. Ohsugi1), Y. Kato, H. Daimon, M. Yoshimaru, T. Imamura,    "Hole Subband Dispersion    in Space Charge Layers under Pb/Si(001) Surfaces Measured by      Angle-Resolved Photoelectron  Spectroscopy"e-J.Surf. Sci. Nanotech. 7 641 (2009) 

We could also see the valence subband dispersion in Si(001).

4. S. N. Takeda, N. Higashi, H. Daimon, "Effect of surface carrier concentration on valence subbands  in Si(111) p-type inversion layers: Angle-resolved photoemission spectroscopy"      Phys. Rev. B 82, 035318 (2010. 

We indicate that the valence subband dispersion shifts rigidly by the gate voltage change.

5. T. Sakata, S. N. Takeda, N. I. Ayob, H. Daimon, "Effect of the Flash Annealing on the Impurity  Distribution and the Electronic Structure in the Inversion Layer",    e-J. Surf. Sci.Nanotech. 13 75 (2015). 

We show that you can not make a sharp inversion layer if you flash anneal the substrate in UHV due to the impurity segregation.

6. N. I. Ayob, S. N. Takeda, T. Sakata, M. Yoshikawa, M. Morita,  H. Daimon,     "Unusual energy separation of subbands in Si(111) p-channels induced by In adsorption"    Jpn. J. Appl. Phys. 54 065702 (2015) 

The measured subband energies does not match with the calculation. 

7. S. N. Takeda, A. Kuwako, M. Nishide, H. Daimon,   "Disentangling hole subbands dispersion in Si(111):     In- and out-of-plane effective masses and   anisotropy"     Phys. Rev. B 93, 125418 (2016)

Complicated subband dispersion is disentangled and compared with the theory.

8. N. I. Ayob, T. Inagaki, H. Daimon, S. N. Takeda, "Empirical potential profile model for subbands with unusual energy separation in Si(111) p-type inversion layer" Jpn. J. Appl. Phys. 60 064004 (2021)

Be careful on narrow p-type inversion layers, they are not the same with the conventional  inversion layers.

 Here are some articles in Japanese.

[1] Hole subband Dispersions in Si Inversion Layers (Silicon Technology 2008)

[2] Semiconductor Quantum Well formed by Surface Structure and its Electronic States  (Kinou Zairyo 2006)