Geoffrey Tse

Tunable band gap in germanene by surface adsorption

Opening a sizable band gap in the zero-gap germanene without heavy loss of carrier mobility is a key issue for its application in nanoelectronic devices such as high-performance field effect transistors (FETs) operating at room temperature. Using the first-principles calculations, we find a band gap is opened at the Dirac point in germanene by single-side adsorption of alkali metal (AM) atoms. This band gap is tunable by varying the coverage and the species of AM atoms, ranging from 0.02 to 0.31 eV, and the maximum global band gap is 0.26 eV. Since the effective masses of electrons and holes in germanene near the Dirac point after surface adsorption (ranging from 0.005 to 0.106me) are small, the carrier mobility is expected not to degrade much. Therefore germanene is a potential candidate of effective FET channel operating at room temperature upon surface adsorption.

Non-linear piezoelectricity in zinc blende GaAs and InAs semiconductors

We investigate the strain dependence of piezoelectric effect, both linear and non linear, in zincblende GaAs and InAs semiconductors. We expanded the polarization in terms of the ionic and dipole charges, internal displacement and the exploited the ab-initio Density Functional Theory (DFT) to evaluate the dependence of all quantities on the strain tensor. By this detailed study of the non linear piezoelectric effect, we report that even third order effects are significant.

A review of non linear piezoelectricity in semiconductors

The piezoelectric effect in polar semiconductor has seen increased interest in recent years because of the prospect of exploiting semiconducting behavior and piezoelectric response, i.e. generating electric fields in response to pressure, in novel optoelectronic devices with applications as pressure sensors and energy harvesting. In this paper we review the basic concepts and recent findings related to the novel concept of non-linear piezoelectricity, which can be exploited in composite nanostructured materials to increase the piezoelectric response compared to bulk materials. Applications to light emitting diodes and nanowires will also be discussed. We will show how the non-linear theory of piezoelectricity can in some cases lead to opposite predictions compared to the classic linear theory.

Non linear piezoelectricity in zincblende GaAs and InAs semiconductors

We investigate the strain dependence of piezoelectric effect, both linear and non linear, in zincblende GaAs and InAs semiconductors. We expanded the polarization in terms of the ionic and dipole charges, internal displacement and the exploited the ab-initio Density Functional Theory (DFT) to evaluate the dependence of all quantities on the strain tensor. By this detailed study of the non linear piezoelectric effect, we report that even third order effects are significant.

Strain dependence of internal displacement and effective charge in wurtzite III-N semiconductors

The elastic and dielectric properties of binary III-N wurtzite semiconductors have been investigated as a function of strain. Using an ab initio density functional theory (DFT), we concentrate on the internal displacement (u) and Born effective charge (Z*) and show that our model provides a unique non linear dependence of the III-N material properties as a function of strain.

Investigating the effect of non linear piezoelectricity on the excitonic properties of III-N semiconductor quantum dots

We investigate the effects of linear and non linear piezoelectricity in wurtzite III-N semiconductors and their influence on the electronic properties of low dimensional quantum dots. By studying the dependence of the biexciton on structural and geometrical parameters of the nanostructure, we show second order to be important particularly when the strain in the nanostructure is reduced

Erratum: Second-order piezoelectricity in wurtzite III-N semiconductors [Phys. Rev. B 84, 085211 (2011)]

We note two typographical errors in our recent paper. First, in Table III, the Lw/Lb ratio in the first row should be 3/5, not 3/50. Second, we gave an incorrect sign for some of the parameters listed in Table IV. The parameters of e311, e333, and e133 in Table IV should read as given here. Because the correct signs were used to calculate the fields in the original work, these corrections do not affect our conclusions.

Erratum: second-order piezoelectricity in wurtzite III-N semiconductors

We note two typographical errors in our recent paper. First, in Table III, the Lw/Lb ratio in the first row should be 3/5, not 3/50. Second, we gave an incorrect sign for some of the parameters listed in Table IV. The parameters of e311, e333, and e133 in Table IV should read as given here. Because the correct signs were used to calculate the fields in the original work, these corrections do not affect our conclusions.

Second-order piezoelectricity in wurtzite III-N semiconductors (vol 84, 085211, 2011)

We note two typographical errors in our recent paper. First, in Table III, the Lw/Lb ratio in the first row should be 3/5, not 3/50. Second, we gave an incorrect sign for some of the parameters listed in Table IV. The parameters of e311, e333, and e133 in Table IV should read as given here. Because the correct signs were used to calculate the fields in the original work, these corrections do not affect our conclusions.