industry news ♦ compound semiconductor ♦ news digest Industry news
InSbN delivers infrared detection July 01, 2010
InSbN photovoltaic infrared detectors offer a promising alternative to the HgCdTe incumbent by combining superior material quality with lower Auger recombination and a range of fabrication techniques.
A team of researchers in Singapore claims to have built the first InSbN-based photodiodes for mid- and long-wavelength infrared detection.
These photovoltaic devices incorporate tiny amounts of nitrogen and produce their strongest photocurrent peak at 5.3 microns, which originates from the binary InSb. Subsidiary peaks in three different samples occurred at 6.30, 6.33 and 6.47 microns.
According to team member Dao Hua Zhang from Nanyang Technology University, one application for these InSbN devices is night vision. In addition, they could be used to detect gases such as sulphur dioxide, ammonia and chlorofluorocarbon refrigerant compounds.
If InSbN detectors are to kick-on and enjoy commercial success, then they needs to take market share from HgCdTe devices that provide detection across the 1 to 25 micron spectral range.
The incumbent technology has many strengths: a tunable bandgap governed by alloy composition; a high optical absorption coefficient; high electron mobility; and readily available doping techniques.
These benefits have to be weighed against several disadvantages, including lattice, surface and interface instabilities of HgCdTe, which can lead to large variations in stoichiometry and transport properties.
“Mass production [of HgCdTe detectors] has a very low uniformity and low yield, and HgCdTe is a highly toxic material,” adds Zhang.
In comparison, InSbN features better material quality and uniformity, thanks to the very small amounts of nitrogen needed to red-shift the bandgap. There are also many options for fabrication, because this ternary can be fabricated by MOCVD, MBE or multi-step ion implantation.
“More importantly, the Auger recombination rate of the InSbN alloy is only one-third of HgCdTe with an equivalent bandgap, which makes InSbN the best candidate for making mid- and long-wavelength infrared photodetectors,” says Wang.
Fabrication of InSbN devices began by depositing a 100 nm-thick, SiN film onto n-type InSb substrates by PECVD. InSbN layers were formed by nitrogen ion implantation, using energies of 90, 180 and 530 keV to ensure a uniform nitrogen profile. The top p-region was then created by magnesium ion implantation.
Annealing the wafers at 550K for 4 hours removed damage caused by implantation, and activated the incorporated nitrogen. Standard photolithography then created mesa-like structures with a 250-micron diameter.
Detectors produced a range of photocurrent spectra, and the longest wavelength device had a photocurrent peak at 6.47 microns and a cut-off wavelength of 9.4 microns. This device has a nitrogen composition of 0.43 percent, according to theoretical band structure calculations with a 10-band k.p model.
Zhang and his colleagues are now planning to build devices spanning the mid and long- wavelength infrared.
July 2010
www.compoundsemiconductor.net 45
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83