**3.2 Growth of group III-Nitride semiconductors**

The first successful synthesis of GaN dates back to as early as 1930s. In 1969, Maruska and Tietjen [38] synthesized single crystalline GaN layers on sapphire substrates by using the technique of hydride vapor phase epitaxy (HVPE). Although most of the III-Nitride semiconductors, especially for industrial-scale production, are usually synthesized via metal–organic chemical vapor deposition (MOCVD), metal–organic vapor phase epitaxy (MOVPE) and HVPE, however, these techniques have some serious drawbacks associated with them. These fabrication methods are generally characterized by quite high growth temperatures (>900°C). Thus, the sample is subjected to a high level of stress when cooled down to the room temperature from such high temperatures. Moreover, the inevitability of such high temperatures has hindered the growth of high-quality InN and its alloys, which are potential candidates for IR and terahertz (THz) optoelectronic applications, due to the dissociation of InN at such high temperatures [16]. There are also various other less-known techniques used for the synthesis of the group III-Nitrides, which are derivatives of the above three methods. However, all these processes involve the treatment and usage of toxic precursors as by-products, and therefore, making

#### **Figure 5.**

*The wurtzite crystal structure of III-nitrides. Nitrogen and group III atoms are represented by gray and yellow spheres, respectively. Figure has been reproduced with permission from Ref. [37].*

**159**

**Figure 6.**

*Group III-Nitrides and Their Hybrid Structures for Next-Generation Photodetectors*

these techniques less environment-friendly and hazardous to human health, which

PAMBE, on the other hand, is a much cleaner synthesis technique and offers the advantage of fabrication of better-quality samples, along with a very important benefit of growth at much lower substrate temperatures when compared with most of its counterparts. MBE is an epitaxial and layer-by-layer growth technique involving precise control of the supply of thermally evaporated atomic species (**Figure 6(a)**). This results into construction of 2D layers on a substrate by means of lattice matching (**Figure 6(b)**). The major advantages of MBE are that it is clean, scalable and highly controlled with a high product quality. The involvement of ultra-high vacuum growth environment and the use of ultra-high purity elements as the source materials, minimize the inclusion of contaminants and impurities in the grown structures. Additionally, with the advent of higher growth rate RF-plasma

*(a) Schematic of a typical MBE system, showing various components. Figure has been adapted with permission from Ref. [40]. (b) Schematic depicting epitaxial growth of a material on a substrate. (c) MBE system located* 

*in materials research Centre, Indian Institute of Science, Bangalore, India.*

*DOI: http://dx.doi.org/10.5772/intechopen.95389*

has become a major concern at the global level.

### *Group III-Nitrides and Their Hybrid Structures for Next-Generation Photodetectors DOI: http://dx.doi.org/10.5772/intechopen.95389*

these techniques less environment-friendly and hazardous to human health, which has become a major concern at the global level.

PAMBE, on the other hand, is a much cleaner synthesis technique and offers the advantage of fabrication of better-quality samples, along with a very important benefit of growth at much lower substrate temperatures when compared with most of its counterparts. MBE is an epitaxial and layer-by-layer growth technique involving precise control of the supply of thermally evaporated atomic species (**Figure 6(a)**). This results into construction of 2D layers on a substrate by means of lattice matching (**Figure 6(b)**). The major advantages of MBE are that it is clean, scalable and highly controlled with a high product quality. The involvement of ultra-high vacuum growth environment and the use of ultra-high purity elements as the source materials, minimize the inclusion of contaminants and impurities in the grown structures. Additionally, with the advent of higher growth rate RF-plasma

#### **Figure 6.**

*Light-Emitting Diodes and Photodetectors - Advances and Future Directions*

at wavelengths ranging from the NIR to the UV.

**3.2 Growth of group III-Nitride semiconductors**

of atom, and with an offset along the c-axis by 5/8 of the cell height. The stacking sequence in the hexagonal structure consists of alternating hexagonal planes of group III and N atom, with a stacking sequence of ABAB [36]. A stick-and-ball model-based diagram of the hexagonal unit cell of III-Nitride semiconductors is shown in **Figure 5**. The group III semiconductors and the nitrogen atoms have been shown in different colors [37]. The polytypes of the III-Nitrides having wurtzite structure, form a continuous alloy system, with direct band gaps ranging from 0.7 eV for InN, 3.4 eV for GaN, and to 6.2 eV for AIN [16]. Therefore, the III-Nitrides are potential candidates for fabrication of optical devices which are active

The first successful synthesis of GaN dates back to as early as 1930s. In 1969, Maruska and Tietjen [38] synthesized single crystalline GaN layers on sapphire substrates by using the technique of hydride vapor phase epitaxy (HVPE). Although most of the III-Nitride semiconductors, especially for industrial-scale production, are usually synthesized via metal–organic chemical vapor deposition (MOCVD), metal–organic vapor phase epitaxy (MOVPE) and HVPE, however, these techniques have some serious drawbacks associated with them. These fabrication methods are generally characterized by quite high growth temperatures (>900°C). Thus, the sample is subjected to a high level of stress when cooled down to the room temperature from such high temperatures. Moreover, the inevitability of such high temperatures has hindered the growth of high-quality InN and its alloys, which are potential candidates for IR and terahertz (THz) optoelectronic applications, due to the dissociation of InN at such high temperatures [16]. There are also various other less-known techniques used for the synthesis of the group III-Nitrides, which are derivatives of the above three methods. However, all these processes involve the treatment and usage of toxic precursors as by-products, and therefore, making

*The wurtzite crystal structure of III-nitrides. Nitrogen and group III atoms are represented by gray and yellow* 

*spheres, respectively. Figure has been reproduced with permission from Ref. [37].*

**158**

**Figure 5.**

*(a) Schematic of a typical MBE system, showing various components. Figure has been adapted with permission from Ref. [40]. (b) Schematic depicting epitaxial growth of a material on a substrate. (c) MBE system located in materials research Centre, Indian Institute of Science, Bangalore, India.*

sources, the synthesis times have been significantly reduced without compromising in the structural quality. One of the earliest works demonstrating growth of GaN by MBE was reported by Yoshida et al. [39] in 1983, wherein they successfully synthesized high electrical and optical quality GaN thin films on sapphire, with an AlN buffer layer via reactive MBE using ammonia as nitrogen source. **Figure 6(c)** shows the MBE setup located in Materials Research Centre, Indian Institute of Science, Bangalore, India.
