Defect Reduction of Ge on Si by Selective Epitaxy and Hydrogen Annealing
| Autor: | Krishna C. Saraswat, Hyun Yong Yu, Ali K. Okyay, Jin-Hong Park |
|---|---|
| Přispěvatelé: | Okyay, Ali Kemal |
| Rok vydání: | 2008 |
| Předmět: |
Capacitor structures
Semiconducting silicon compounds Silicon Dislocation densities Materials science Selective depositions Nucleation chemistry.chemical_element Defect reductions Si CMOS Substrate (electronics) Epitaxy Semiconducting germanium compounds Surface roughness Epitaxial growth Hetero epitaxies Silicon alloys Diode MOS capacitors Monolithic integrations Germanium business.industry Schottky diode Selective epitaxies High qualities chemistry Monolithic integrated circuits Optoelectronics AFM Hydrogen annealing Dislocation In-situ doping business Hydrogen |
| Zdroj: | ECS Transactions |
| ISSN: | 1938-6737 1938-5862 |
| Popis: | We demonstrate a promising approach for the monolithic integration of Ge-based nanoelectronics and nanophotonics with Silicon: the selective deposition of Ge on Si by Multiple Hydrogen Annealing for Heteroepitaxy (MHAH). Very high quality Ge layers can be selectively integrated on Si CMOS platform with this technique. We confirm the reduction of dislocation density in Ge layers using transmission electron microscope (TEM) analysis and Schottky diode electrical behavior. In addition, the analysis of the growth directions and the geometrical shape of the resulting films based on the growth conditions provide further insight to the selective Ge growth mechanism At 400C, the growth in the direction is dominant while directional facets are observed giving the film a characteristic trapezoidal shape. This is primarily due to the relatively slow growth rate along the direction at these conditions, and it can be explained by surface migration (Fig 1(a)). As the deposition time is increased, the layer forms into a pyramid-like structure. Once the full pyramid is formed, the film thickness does not increase significantly with further growth time. This can explain the difference in the film thicknesses grown in varying dimensions of SiO2 windows. However, in Figure 1(b), a different shape is observed when films are grown at 600C due to high growth rates in both the direction (94 nm/min) and the direction (480 nm/min). This shape is attributed to restricted surface migration by an excessive number of nucleation centers[1]. We analyzed the threading dislocations in the grown films. In Figure 2, it is clearly shown that most of dislocations are at the Ge/Si interface and the surface of the film has low defect density due to the hydrogen annealing[2]. The threading dislocations A, B, and C show that they change direction and terminate at the surface normal to the facet that occurred due to the selective growth. Therefore the density of dislocations is reduced due to combined mechanism of hydrogen annealing and the selective growth. The current-voltage characteristic of the Schottky diode is also an indication of material quality[3]. Figure 3(b) shows the metal semiconductor(MS) (Ti-Ge) Schottky diode I-V characteristics with 400 C and 500 C multistep growth on a10μm x10μm selective area followed by hydrogen annealing. The I-V characteristic of the Ti-Ge junction shows a Schottky diode behavior with decent rectification which is another indication of the low defect density of the selective MHAH-Ge substrate. At -1V, a diode leakage current 10.15nA is observed. In conclusion, high quality Ge can be selectively grown on Si by MHAH with a SiO2 masking pattern. Two different growth mechanisms were observed at 400C and 600C resulting from relative growth rates in and directions. The hydrogen annealing and the selective growth can be used to reduce the dislocation density and the surface roughness. (a) (b) |
| Databáze: | OpenAIRE |
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