Application areas

The unique properties of group III-nitride compound semiconductors, e.g. AlN, GaN, InN and their alloys, inspired many advanced device designs/structures, integrating electrical, optical, and magnetic functionalities. Ultimately, the usefulness of indium nitride and group III-Nitride alloys depends on the determination of the band gap. A higher band gap preferred for microwave transistor devices, a smaller band gap is preferable for a full solar spectrum cell based on InGaN applications.

1.3.2.1 Optical applications

Electronic lightning technology become important with the invention55 of first light

emitting diode LEDs in 1962. Following the achievement of LED technology, light

amplification by stimulated emission (LASER) was demonstrated56,57 in a semiconductor

by 4 groups. Development of semiconductors allowed the production of bright light emitters that are used in optical fiber networks, data storage (Compact-Disc Technology),

and document printing (Laser printers). But LEDs based on GaAs operate only in the red to yellow portion of the spectrum. SiC has been used for the fabrication of blue LEDs. However SiC or II-VI based LEDs were not emitting with enough intensity due to their indirect band gap. The first blue LEDs based on the III-V nitrides were made commercially available by Nichia in early 1994. Much research has been done on III- Nitrides comprising the Al-Ga-In-N alloys and show great promise for meeting the next generation optical applications.

1.3.2.2 LED applications

InN is important as a component of group III-Nitrides (Ga1-y-xAly Inx)N enabling the

fabrication of high-efficient light emitting diodes in a wide spectral region, depending on the composition at room temperature. As shown in Figure 1.4, (Ga1-y -xAly Inx)N alloys

system span a wide range of band gap energies from 1 eV to 6.2 eV which correspond to wavelengths ranging from near infrared to deep ultraviolet. In addition, the band gap of the Group III-N system is direct, leading to high quantum efficiency and faster switching speeds. Nakamura and his colleagues demonstrated the first blue/green light emitting

diode based on InGaN. The structure consisted of a 3 nm layer In0.2Ga0.8N sandwiched

between p-type AlGaN and n-type GaN, all grown on sapphire substrate58. Achieving a

red light emitting diode based on InGaN structures depends on indium rich InGaN heterostructures. White LEDs have been developed recently by coating GaN LED with

phosphorus59 which produces light that appears white. However this structure is not as

efficient as the commercial fluorescent light sources. Combining red light emitting diodes with blue/green ones having the same power and brightness can produce full color displays and efficient white lamps.

Researchers at IBM60 demonstrated an InN nanowire LED, which emits infrared light. The nanowires emit infrared light, which makes them ideal for optical communications between devices on microchips that would speed up the computers drastically. If the mechanism in InN nanowires can be tuned to emit red, green and blue light, all nanowire LEDs could be manufactured on the same substrate. That could make LEDS even cheaper and lead to the devices with improved performance.

Figure 1. 4 Band gap energy vs. lattice constant for binary group III-Nitrides material systems.

1.3.2.3 Laser applications

Fabrication of high quality of LEDs enables the fabrication of semiconductor lasers that operate at light wavelengths from ultraviolet to the green. The advantage of blue GaN/InGaN lasers with shorter wavelength (405 nm) than a red laser (605 nm) allows five times more storage capacity (25 GB) over traditional DVDs. Blu-ray disc technology was recently adopted by a group of world leading consumer electronics (including Apple, Dell, HP, JVC, LG, Mitsubishi, Samsung, Sharp, Philips, Pioneer and

Sony Corp.) which enable recording and rewriting61. The impressive accomplishments

taking place and opening a variety of potential markets such as blu-ray are only the beginning of the application of this technology. The performance issues that are related to the crystal growth itself limit further development. It is possible to mix the Al, Ga, and In ratios to make ternary and quaternary alloys such as (Ga1-y -xAly Inx) N. It is therefore

possible, in principle, to make semiconductor lasers that emit light from the deep ultraviolet with a photon energy of 6 eV, to the infrared with photon energy of 1 eV. However, only a much narrower range of operation from the near ultraviolet (3.5 eV) to the green (2.4 eV) has been demonstrated.

InN one dimensional (1D) nanostructures, such as nanowires, nanorods, nanotubes and nanobelts are currently the most attractive structures due to the easier growth in single crystal forms without defects, and lasing in the crystals could be expected62. Hu et al.62 reported the investigation of infrared lasing in high quality single-

crystalline InN nanobelts grown by MOCVD. This can be considered a “major advance “ in the nanophotonics field and will impact imaging in chemistry biology, and optical communications.

1.3.2.4 Electronic applications

Small effective electron mass, large polar optical phonon energy31, high electron

mobilities close to the theoretical calculated mobility values32 make InN a promising

device for electronic applications. Nevertheless, theoretical calculations by O’Leary et

al.30,31,63 also suggest that InN has superior electrical properties compared to GaN. As

shown in Figure 1.5, InN achieves the highest steady-state peak drift velocity ~5×107

cms-1 which is considerably larger than that of other III-Nitrides and of GaAs. The

calculated electron mobility of InN by Chin et al. 34 is 4400 cm2/Vs for room

temperature. The highest electron mobility measured at room temperature is 3500 cm2/Vs35. Thus, InN based devices offer great potential for high-speed, high performance heterojunction FETs as compared to GaAs based HFETs for both power and frequency response. Wide band gaps enable the application of high supply voltages and also allow

the material to withstand high operating temperatures (300° C and 500° C). AlInN might

be a good candidate64for high-power/high temperature microwave applications because

of its higher breakdown voltage.

The current state of the solar cell with 30% percent efficiency are produced from

the following materials: Ge (0.66 eV), GaAs (1.43 eV) and GaInP (1.9 eV)65,66. For the

specific case of In1-xGaxN varying x values (x≤ 0.63) produces band gaps between 0.7

and 1.9 eV which will cover the whole solar spectrum from infrared to UV. The possibility of designing and fabricating multi-junction solar cells using a single ternary alloy system is attractive. Since space based systems represent the primary application of MJ solar cells, radiation resistance is crucial. It has been shown that InN and InGaN are 2 times more resistant under extraordinary particle radiation67.

Figure 1. 5 Calculated steady-state drift velocity as function of electric field in group III-Nitride materials and GaAs. In all cases, O’Leary et al.30 assumed a doping concentration of 1017 cm-3 and crystal temperature of 300 K.