# Formation of a Thin Continuous GaSb Film on Si(001) by Solid Phase Epitaxy

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

_{2}layer [11]), or the formation temperature of the GaSb film is significantly decreased (down to 200 °C) [6]. Lowering of the formation temperature allows not only the suppression of the Ga surface diffusion, but also reduction of Sb desorption during the MBE process. Provided a low growth temperature is used, one can reduce the Sb/Ga molecular flux ratio from 8.5–10 at a growth temperature of 560–600 °C [10,12] down to 5 at 200 °C [6]. To further reduce the surface diffusion of Ga atoms during GaSb film formation, solid-phase epitaxy (SPE) can be used instead of MBE. In the SPE process, the deposition of the Ga–Sb mixture occurs on an unheated substrate. In this case, since no desorption of Sb occurs [14] and Ga diffusion is strongly suppressed, Ga and Sb can be deposited in a 1:1 ratio.

_{rms}) is 1.74 nm. At the same time, a 14-nm-thick GaSb film does not withstand annealing at 300 °C and aggregates into connected islands.

## 2. Materials and Methods

^{−11}Torr. The chamber was equipped with an Auger electron spectroscopy (AES) unit that could record the spectra of electron energy loss spectroscopy (EELS), and with a low-energy electron diffraction (LEED) unit. The substrate temperature was controlled by an infrared pyrometer. Gallium and Sb deposition rates (~0.34 nm/min) were calibrated using LEED patterns of known surface reconstructions of Ga and Sb on Si(001) [15,16]. Native oxide was removed from the substrate surface by annealing at 1160 °C for 20 min, and as a result, the surface reconstruction Si(001)2 × 1 was formed; contamination of the surface was below the detection limit of AES.

## 3. Results and Discussion

^{−1}on the spectra in the far infrared (FIR) spectral region (Figure 1). The observed peak corresponds to the longitudinal optical phonon (LO) [19] in the GaSb cubic lattice (F-43m). The peak at 612 cm

^{−1}comes from the silicon substrate (Figure 1). One can see that a decrease in the thickness of the GaSb film from 20 down to 14 nm resulted in a significant decrease (about four-fold) in the intensity of the 225 cm

^{−1}peak, which is due to the aggregation of the GaSb film on the sample A surface during the annealing at 300–500 °C (see the discussion of the AES, LEED, and AFM data obtained for sample A).

^{10}cm

^{−2}; their average lateral size is 50 nm and height is 21.3 nm. Because of agglomeration, the 14-nm-thick GaSb film became very rough, with σ

_{rms}= 7.05 nm. The discontinuity of the film is also confirmed by the FIR absorption spectroscopy data: a low intensity of the peak at 225 cm

^{−1}was caused by the decrease in GaSb film surface coverage (Figure 1). Summarizing the results obtained for sample A, we can state that: (i) the 14-nm-thick GaSb film was continuous after annealing at 200–250 °C, (ii) the GaSb film agglomeration took place during annealing at 300–500 °C, (iii) there is no significant GaSb film aggregation at 300 °C, and (iv) the GaSb film thickness of 14 nm is not sufficient to withstand annealing at temperatures of 300 °C and higher.

^{3}= 1.41 × 10

^{23}cm

^{−3}is the valence electrons’ concentration in the ideal cubic GaSb, and n and p are the electron and hole concentrations in relaxed single-crystal GaSb, respectively. It was found that Czochralski-grown unintentionally p-doped relaxed single-crystal GaSb has hole concentration p ≈ 1.3 × 10

^{17}cm

^{−3}[23]. Therefore, we can assume that for this p-doped relaxed single-crystal GaSb, n << p << ${n}_{v}^{ideal}$, and hence ${n}_{v}^{sc}$ ≈ ${n}_{v}^{ideal}$ = 1.41 × 10

^{23}cm

^{−3}, while the energy of the bulk plasmon of the GaSb single crystal $\mathrm{\hslash}{\omega}_{p}^{sc}$ = 14.7 eV [17,20]. We placed these values of $\mathrm{\hslash}{\omega}_{p}^{sc}$ and ${n}_{v}^{sc}$ in Equation (2) and obtained A = 3.91 × 10

^{‒11}eV·cm

^{3/2}.

^{23}cm

^{−3}—the value is calculated by Equation (1)) compared to the ideal GaSb structure. The change in the valence electron concentration n

_{v}, and hence the shift energy of the bulk plasmon (e.g., 0.3 eV for plasmon energy of 15 eV), can originate from a change in the unit cell volume as a result of deformation.

^{18}cm

^{−3}. It is higher than that in single crystal GaSb, but it is much less than the concentration of valence electrons of GaSb ${n}_{v}^{ideal}$ = 1.41 × 10

^{23}cm

^{−3}. Therefore, the contribution of the hole concentration p to ${n}_{v}$ is very small, so we ignored it. The number of valence electrons, N, is obtained from the formula for an ideal crystal ${n}_{v}^{ideal}=N/{a}^{3}$; then

^{−4}%. It is very small value, so we neglected it. According to our assessment, during the GaSb mixture deposition, the substrate was gradually heated by Ga and Sb sources up to 170 °C at the end of the deposition process. This temperature is sufficient for the crystallization of the GaSb mixture [24], therefore GaSb crystals appeared in the film during deposition. During the crystallization, noticeable compression of the GaSb lattice (1.33%) occurs. Further annealing at 200 °C did not change the bulk plasmon energy (Figure 3a), and so it did not change the value of GaSb lattice deformation. We suppose that raising the temperature by 30 °C (up to 200 °C) cannot lead to remarkable recrystallization and reduce the deformation of the GaSb lattice. An increase in the annealing temperature up to 300 °C results in a decrease of the bulk plasmon energy (14.7 eV). This value of bulk plasmon energy corresponds to the relaxed GaSb film. Thus, the annealing at a temperature of 300 °C reduces the deformation in the GaSb film that was induced in the film during its crystallization.

_{rms}= 1.74 nm (Table 1), which is much lower than that obtained for GaSb films grown by MBE on clean silicon (σ

_{rms}≈ 35 nm, at a film thickness of ≈20 nm) [5] and an AlSb buffer layer (σ

_{rms}≈ 5–6 nm) [5]. The surface relief development during GaSb MBE growth arises from a large Ga surface diffusion coefficient, while in the case of SPE, Ga, and Sb atoms intermixed enough to form small crystalline grains at the very beginning of the annealing, at about 200 °C. The increase of the annealing temperature results in grain size growth, but without noticeable development of the film roughness.

_{1}V

_{1}W

_{1}] and Si[UVW] of 2D cells of GaSb and Si, was calculated by the following equation:

_{1}V

_{1}W

_{1}] of the 2D GaSb lattice; ${b}_{\left[UVW\right]}^{Si}={a}_{Si}\sqrt{{U}^{2}+{V}^{2}+{W}^{2}}$ is the length of vector [UVW] of the 2D Si lattice; a

_{GaSb}and a

_{Si}are the lattice constants of GaSb and Si, respectively. The b values are shown in Figure 5a,b. The ER for area 4, GaSb$\left(111\right)$||Si$\left(111\right)$ and GaSb$\left[1\overline{1}0\right]$||Si$\left[1\overline{1}0\right]$, is common for MBE-grown GaSb, while the ER for area 1, GaSb$\left(111\right)$||Si$\left(11\overline{1}\right)$ and GaSb$\left[11\overline{2}\right]$||Si$\left[1\overline{1}0\right]$, was observed only for SPE-grown GaSb; below, we will refer to this ER as GS$\left[11\overline{2}\right]$. It attracted our attention because of a small discrepancy between the GaSb and Si (−2.7%) lattices in the direction of GaSb$\left[11\overline{2}\right]$ (lattice vectors GaSb$\left[11\overline{2}\right]$ and Si$\left[2\overline{2}0\right]$ in Figure 5a).

## 4. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Spectral dependence of transmittance in the far infrared (FIR) region for the silicon substrate and samples A and B.

**Figure 2.**The evolution of the Auger spectra in the process of sample A formation; the inset is a dependence of the intensity of the silicon peak (92 eV) on the annealing temperature (the minimal temperature in the inset is the temperature of the Ga–Sb mixture after deposition) (

**а**); atomic force microscopy (AFM) image of sample A after the final annealing at 500 °C for 15 min; the inset is a 1 × 1 LEED pattern that appears after annealing of the film at 300 °C for 15 min (

**b**).

**Figure 3.**Evolution of the spectra of electron energy loss spectroscopy (EELS) spectra in the process of sample B formation (

**a**); AFM image of sample B after the final annealing at 300 °C for 20 min (

**b**).

**Figure 4.**TEM images of the cross-section of sample B; squares 1–5 mark areas with individual GaSb grains, which have an interface with the substrate (

**a**); in the insets one can see the fast Fourier transform (FFT) filtered image of area 1 and a magnified image of the interface between GaSb grain in area 1 and the substrate (magenta frame). The FFT pattern taken from the silicon substrate (

**b**), and from areas 1, 2, and 5, respectively (

**c**–

**e**). Spots marked by green and magenta circles in FFT patterns are produced by GaSb grains not presented in Table 2.

**Figure 5.**The arrangement of atoms on the GaSb/Si(001) interface for the following ERs: GaSb$\left(111\right)$||Si$\left(11\overline{1}\right)$ and GaSb$\left[11\overline{2}\right]$||Si$\left[1\overline{1}0\right]$ (

**a**) and GaS$\left(111\right)$||Si$\left(111\right)$ and GaSb$\left[1\overline{1}0\right]$||Si$\left[1\overline{1}0\right]$ (

**b**). The lattice mismatch М is shown in parentheses after the length of the GaSb lattice vector.

Sample | GaSb Mixture Thickness, nm | Time of Deposition, min | Annealing Mode | σ_{rms}, nm | GaSb Islands | ||
---|---|---|---|---|---|---|---|

Concentration, ×10^{10} cm^{−2} | Height, nm | Lateral Size, nm | |||||

A | 14 | 20 | 200–500 °C (step 50 °C)— for 15 min | 7.05 | 4.3 | 21.3 | 50 |

B | 20 | 30 | 200 °C—15 min, 300 °C—20 min | 1.74 | – | – | – |

**Table 2.**The epitaxial relationships observed for GaSb grains in the film of sample B that have an interface with silicon substrate.

Area | Epitaxial Relationships | Angle of Disorientation with Substrate | Deformation of the GaSb Lattice | MBE Method |
---|---|---|---|---|

1 | GaSb$\left(111\right)$||Si$\left(11\overline{1}\right)$ ^{a} GaSb$\left[11\overline{2}\right]$||Si$\left[1\overline{1}0\right]$ ^{a} | 0 | −0.61% | - |

2 | GaSb$\left(113\right)$||Si$\left(11\overline{1}\right)$ ^{a} GaSb$\left[1\overline{1}0\right]$||Si$\left[1\overline{1}0\right]$ ^{a} | 2.0 | −0.38% | - |

3 | GaSb$\left(11\overline{1}\right)$||Si$\left(002\right)$ ^{a} GaSb$\left[1\overline{1}0\right]$||Si$\left[1\overline{1}0\right]$ ^{a} | 1.8 | −1.73% | - |

4 | GaSb$\left(111\right)$||Si$\left(111\right)$ ^{a} GaSb$\left[1\overline{1}0\right]$||Si$\left[1\overline{1}0\right]$ ^{a} | 0 | −2.58% | GaSb$\left\{002\right\}$||Si$\left\{002\right\}$ ^{b} GaSb$\langle 110\rangle $||Si$\langle 110\rangle $ ^{b} GaSb$\left(111\right)$||Si$\left(111\right)$ ^{c} GaSb$\left[1\overline{1}0\right]$||Si$\left[1\overline{1}0\right]$ ^{c} |

5 | GaSb$\left(220\right)$||Si$\left(11\overline{1}\right)$ ^{a} GaSb$\left(111\right)$||Si$\left(220\right)$ ^{a} GaSb$\left[1\overline{1}0\right]$||Si$\left[1\overline{1}0\right]$ ^{a} | 0 | −2.00% | GaSb$\left\{111\right\}$||Si$\left\{220\right\}$ ^{b} GaSb$\langle 110\rangle $||Si$\langle 110\rangle $ ^{b} |

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## Share and Cite

**MDPI and ACS Style**

Chusovitin, E.; Dotsenko, S.; Chusovitina, S.; Goroshko, D.; Gutakovskii, A.; Subbotin, E.; Galkin, K.; Galkin, N.
Formation of a Thin Continuous GaSb Film on Si(001) by Solid Phase Epitaxy. *Nanomaterials* **2018**, *8*, 987.
https://doi.org/10.3390/nano8120987

**AMA Style**

Chusovitin E, Dotsenko S, Chusovitina S, Goroshko D, Gutakovskii A, Subbotin E, Galkin K, Galkin N.
Formation of a Thin Continuous GaSb Film on Si(001) by Solid Phase Epitaxy. *Nanomaterials*. 2018; 8(12):987.
https://doi.org/10.3390/nano8120987

**Chicago/Turabian Style**

Chusovitin, Evgeniy, Sergey Dotsenko, Svetlana Chusovitina, Dmitry Goroshko, Anton Gutakovskii, Evgeniy Subbotin, Konstantin Galkin, and Nikolay Galkin.
2018. "Formation of a Thin Continuous GaSb Film on Si(001) by Solid Phase Epitaxy" *Nanomaterials* 8, no. 12: 987.
https://doi.org/10.3390/nano8120987