Industries such as the automotive, aerospace or military, as well as environmental and biological research have promoted the development of ultraviolet (UV) photodetectors capable of operating at high temperatures and in hostile environments. UV-enhanced Si photodiodes are hence giving way to a new generation of UV detectors fabricated from wide-bandgap semiconductors, such as SiC, diamond, III-nitrides, ZnS, ZnO, or ZnSe. This paper provides a general review of latest progresses in wide-bandgap semiconductor photodetectors.

https://iopscience.iop.org/article/10.1088/0268-1242/18/4/201/pdf

Wide-bandgap semiconductor ultraviolet photodetectors

Ordered growth of neurons on diamond

The use of nanodiamond monolayer coatings to promote the formation of functional neuronal networks.

High-quality single-crystal diamond films, homoepitaxially grown by microwave chemical vapor deposition, have been used to produce diamond-based photodetectors. Such devices were tested over a very wide spectral range, from the extreme ultraviolet (UV) (20 nm) up to the near IR region (2400 nm). An optical parametric oscillator tunable laser was used to investigate the 210–2400 nm spectral range in pulse mode. In this region, the spectral response shows a UV to visible contrast of about 6 orders of magnitude. A time response shorter than 5 ns, i.e., the laser pulse duration, was observed. By integrating the pulse shape, a minor slow component was evidenced, which can be explained in terms of trapping–detrapping effects. Extreme UV gas sources and a toroidal grating vacuum monochromator were used to measure the device response down to 20 nm in continuous mode. In particular, the extreme UV He spectrum was measured and the He II m, 30.4 nmand He I 58.4 nm emission lines were clearly detected. The measured t...

Extreme ultraviolet single-crystal diamond detectors by chemical vapor deposition

Polycrystalline diamond films have been found to display p-type surface conductivity. No bulk impurity is added to the films; the p-type characteristics of the undoped diamond are thought to be due to a surface or near surface hydrogenated layer. Carrier concentrations within the range 1017–1019 cm−3 have been measured; control over the carrier concentration can be achieved by annealing the “as-grown” films in air. For a given annealing temperature a stable carrier concentration arises. The Hall carrier mobility has been explored and a value of >70 cm2/Vs has been measured for a film with a carrier concentration of ∼5×1017 cm−3, the highest reported for polycrystalline thin film diamond and equivalent to boron doped single crystal diamond.

High carrier mobility in polycrystalline thin film diamond

Photoconductive properties of thin film diamond

Auger electron spectroscopy was used to analyze polycrystalline thin‐film diamond surfaces following the use of differing methods for the removal of unwanted nondiamond carbon. Exposing the film to a hydrogen plasma at the termination of the growth process is effective for producing a surface that gives an Auger spectrum typical of diamond with little contamination. Strongly oxidizing solutions involving sulfuric acid generate low concentrations of surface sulfur together with an oxide phase. However, in the case of an ammonium persulfate–sulfuric acid etchant solution, the Auger features associated with the diamond more closely resemble those of single crystal material suggesting that this treatment may offer better performance when used during the fabrication of thin‐film diamond electronic devices.

Bhaswar Baral

Papers

Photoconductive properties of thin film diamond

Cleaning thin-film diamond surfaces for device fabrication: An Auger electron spectroscopic study

Enhancing low field electron emission from polycrystalline diamond

Dopant incorporation mechanisms during the growth of thin film diamond

Interaction of organo-sulfur compounds with CVD diamond surfaces