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Dynamic probe of ZnTe(110) surface by scanning tunneling microscopy

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ABSTRACT

The reconstructed surface structure of the II–VI semiconductor ZnTe (110), which is a promising material in the research field of semiconductor spintronics, was studied by scanning tunneling microscopy/spectroscopy (STM/STS). First, the surface states formed by reconstruction by the charge transfer of dangling bond electrons from cationic Zn to anionic Te atoms, which are similar to those of IV and III–V semiconductors, were confirmed in real space. Secondly, oscillation in tunneling current between binary states, which is considered to reflect a conformational change in the topmost Zn–Te structure between the reconstructed and bulk-like ideal structures, was directly observed by STM. Third, using the technique of charge injection, a surface atomic structure was successfully fabricated, suggesting the possibility of atomic-scale manipulation of this widely applicable surface of ZnTe.

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(a) Normalized differential conductance (NDC)—sample bias voltage spectra obtained above a Zn atom (blue) and a Te atom (red). The setpoint voltage and current were Vs = −2.0 V and It = 20 pA, respectively. The peaks shown in the blue (+1.0 eV) and red (−0.8 eV) lines indicate the energy levels of the dangling bond states of the surface Zn and Te atoms, respectively. (b) Schematic of the ZnTe band structure derived from the NDC-Vs spectra.
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Figure 2: (a) Normalized differential conductance (NDC)—sample bias voltage spectra obtained above a Zn atom (blue) and a Te atom (red). The setpoint voltage and current were Vs = −2.0 V and It = 20 pA, respectively. The peaks shown in the blue (+1.0 eV) and red (−0.8 eV) lines indicate the energy levels of the dangling bond states of the surface Zn and Te atoms, respectively. (b) Schematic of the ZnTe band structure derived from the NDC-Vs spectra.

Mentions: To investigate the surface electronic structure in more detail, we carried out STS measurement. Figure 2 shows the results of normalized differential conductance (NDC) analysis, which reflects the local density of states (LDOS). NDC-Vs curves were measured on topmost Zn (blue) and Te (red) atoms, respectively. There are differences between the two curves, particularly at the rising edges from the semiconductive gap region near Vs = 0. At the rising edge at a positive (negative) sample bias voltage, the NDC-Vs spectrum obtained at the Zn (Te) position exhibits a higher peak than that obtained at the Te (Zn) position. These results can be comprehensively explained by the mechanism that the empty and occupied dangling bond states are formed through the charge transfer from cationic Zn to anionic Te associated with the surface reconstruction. Similar charge transfer is well known to occur on several semiconductor surfaces such as Si(100) dimer and GaAs(110) reconstructed surfaces, which has been confirmed by STM observation with atomic resolution [13, 14]. The STS analysis has confirmed the surface states of ZnTe(110) in the real space. The observed energy levels correspond to the surface states studied by ARPES [10], EELS [11], and DFT [12], which have suggested that the anionic Te (cationic Zn) dangling bond state is located near the valence band maximum (conduction band minimum), as shown in figure 2(b). Here, the energy gap of the host ZnTe was determined from the distance between the Zn (−1.0 V) and Te (+1.3 V) peaks in the spectra, because we have to remove the influence of their surface states. The gap energy obtained is about 2.3 eV, which is close to the previously reported energy gap of ZnTe (2.39 eV at 4.2 K).


Dynamic probe of ZnTe(110) surface by scanning tunneling microscopy
(a) Normalized differential conductance (NDC)—sample bias voltage spectra obtained above a Zn atom (blue) and a Te atom (red). The setpoint voltage and current were Vs = −2.0 V and It = 20 pA, respectively. The peaks shown in the blue (+1.0 eV) and red (−0.8 eV) lines indicate the energy levels of the dangling bond states of the surface Zn and Te atoms, respectively. (b) Schematic of the ZnTe band structure derived from the NDC-Vs spectra.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036505&req=5

Figure 2: (a) Normalized differential conductance (NDC)—sample bias voltage spectra obtained above a Zn atom (blue) and a Te atom (red). The setpoint voltage and current were Vs = −2.0 V and It = 20 pA, respectively. The peaks shown in the blue (+1.0 eV) and red (−0.8 eV) lines indicate the energy levels of the dangling bond states of the surface Zn and Te atoms, respectively. (b) Schematic of the ZnTe band structure derived from the NDC-Vs spectra.
Mentions: To investigate the surface electronic structure in more detail, we carried out STS measurement. Figure 2 shows the results of normalized differential conductance (NDC) analysis, which reflects the local density of states (LDOS). NDC-Vs curves were measured on topmost Zn (blue) and Te (red) atoms, respectively. There are differences between the two curves, particularly at the rising edges from the semiconductive gap region near Vs = 0. At the rising edge at a positive (negative) sample bias voltage, the NDC-Vs spectrum obtained at the Zn (Te) position exhibits a higher peak than that obtained at the Te (Zn) position. These results can be comprehensively explained by the mechanism that the empty and occupied dangling bond states are formed through the charge transfer from cationic Zn to anionic Te associated with the surface reconstruction. Similar charge transfer is well known to occur on several semiconductor surfaces such as Si(100) dimer and GaAs(110) reconstructed surfaces, which has been confirmed by STM observation with atomic resolution [13, 14]. The STS analysis has confirmed the surface states of ZnTe(110) in the real space. The observed energy levels correspond to the surface states studied by ARPES [10], EELS [11], and DFT [12], which have suggested that the anionic Te (cationic Zn) dangling bond state is located near the valence band maximum (conduction band minimum), as shown in figure 2(b). Here, the energy gap of the host ZnTe was determined from the distance between the Zn (−1.0 V) and Te (+1.3 V) peaks in the spectra, because we have to remove the influence of their surface states. The gap energy obtained is about 2.3 eV, which is close to the previously reported energy gap of ZnTe (2.39 eV at 4.2 K).

View Article: PubMed Central - PubMed

ABSTRACT

The reconstructed surface structure of the II–VI semiconductor ZnTe (110), which is a promising material in the research field of semiconductor spintronics, was studied by scanning tunneling microscopy/spectroscopy (STM/STS). First, the surface states formed by reconstruction by the charge transfer of dangling bond electrons from cationic Zn to anionic Te atoms, which are similar to those of IV and III–V semiconductors, were confirmed in real space. Secondly, oscillation in tunneling current between binary states, which is considered to reflect a conformational change in the topmost Zn–Te structure between the reconstructed and bulk-like ideal structures, was directly observed by STM. Third, using the technique of charge injection, a surface atomic structure was successfully fabricated, suggesting the possibility of atomic-scale manipulation of this widely applicable surface of ZnTe.

No MeSH data available.