Bandgap of diamond

The size of the bandgap can vary from a fraction of an eV (in the IR region of the spectrum) to ca. 4 eV or more (wide-bandgap semiconductors). The upper limit is somewhat arbitrary a substance commonly thought of as an insulator such as diamond has a large bandgap of 5.5 eV, but it can nevertheless be doped with elements such as B, N, or P to become an electrically-conducting semiconductor. 

Regarding the structure of nanodiamond, a distinction has to be made between the diamond core that usually features a cubic lattice and, on the other hand, the surface. Depending on particle size, the portion of surface atoms may amount to as much as 50%. Generally the surface structure plays a major role for the material properties observed. At particle dimensions of more than 2nm, the bandgap of nanodiamond corresponds to that of macroscopic diamond. Quantum effects are not observed, but there are interband states that can be attributed to partial surface graphitization and lattice defects, respectively. 

The luminescence characteristics of diamond films are also strongly affected by the presence of defects. Although it requires considerable energies, an excitation across the entire bandgap is possible. It may be effected by (laser) light, by an... 

Due to the wide bandgap, the conduction band of diamond approximates the vacuum level. Consequently, electrons excited into the conduction band may leave the diamond s surface as there is no significant potential difference between conduction band and vacuum level. In hydrogenated diamond films, the conduction band is even observed to exceed the vacuum level, resulting in a negative electron affinity of the respective film. This causes the emission of excited electrons from the film to occur all the easier. 

Fig. 39. (a) Calculated bandgap for diamond as a function of applied pressure for the case of hydrostatic compression and for compression along the fourfold axis of diamond (combined shear and hydrostatic) [175] and (b) the measured hardness values of diamond in the indentation in [001] direction [192] (experimental data from References [193] (filled circles), [194] (open squares), and [195] (open circles)). 

Visible luminescence is a well-known optical property of single crystal diamond particularly in the blue and green regions. This luminescence originates in the states at mid-bandgap and is caused by impurities and lattice defects. Cathodoluminescence (CL) is another characteristic of diamond. The CL of single crystal diamond is described as a band-A luminescence and the peak of the spectra is found between 2.4 and 2.8 eV (from green to purple-blue).f 2M lf J... 

Pure single-crystal diamond, with a bandgap of 5.48 eV, is one of the best solid electrical insulators (see Sec. 6.2).l l The high strength of the... 

The semiconductor properties of diamond are excellent and it has good potential as a semiconductor material. i It is an indirect bandgap semiconductor and has the widest bandgapof any semiconductor (see Sec. 6.2). 

Silicon is active as a UV photodiode, but wide-bandgap semiconductors are considered to be more useful as DUV optical sensors because of their superior signal to noise (SN) ratios and their stability. Recently, a highly oriented diamond film with a bandgap of 5.5 eV was demonstrated as a DUV-FUV sensitive detector... 

Pleskov et al. made the first extensive study of diamond electrodes [2]. The electrodes were un-doped, but had sufficient conductivity, most likely from defects, for electrochemical measurements. They found a photoresponse at sub bandgap wavelengths, which they attributed to excitation of electrons from mid-gap states to the conduction band. Sakharova et al. made early impedance studies of diamond electrodes [3]. 

Other wide bandgap materials, such as GaN, AIN, and diamond, with band-gaps of 3.4, 6.3, and 5.5 eV, respectively, have also been explored by a number of... 

Preliminary results were recently reported [145] on the use of CdTe electrodeposition on diamond in the fabrication of a solid-state solar cell based on the boron-doped p-type diamond/n-type CdTe junction. In this cell, the wide-bandgap diamond is an optical window that generates photovoltage, whereas the narrow-bandgap CdTe generates photocurrent. We note that no appropriate p-type material for the fabrication of optical windows has existed so far therefore, one would use an n-type CdS window coupled with narrow-bandgap p-type CdTe. However, the pro-... 

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