Burstein-Moss

CdO, the first discovered and applied transparent conductor [40], which also exhibits the highest reported conductivity (see compilation of data in [41]), is less used today because of its toxicity and its low optical band gap (EStPhotoelectron spectra indicate, however, that the band gap is 1 eV [43]. Although the (direct) optical gap is increased for degenerate doping due to the Burstein-Moss effect [44], it remains difficult to prepare noncolored CdO films. 

However, in some cases, a discrepancy with respect to Burstein-Moss theory has been experimentally observed Roth et al. [41,42] have studied absorption effects in heavily-doped ZnO hlms. They observed that for N > 3 x 1019 cm-3, a shrinkage effect of the gap occurs in addition to the Burstein-Moss effect. This shrinkage of the gap is due to the merging of the donor and... 

Fig. 6.42. Energy band gap as a function of N2/3 (N being the carrier density) for AP-CVD ZnO B films deposited at 375° C from DEZ, ethanol, and different diborane concentrations. The linear fitting curve is in good accordance with the Burstein-Moss model. Reprinted with permission from [28]...

Fig. 6.43. Variation of band gap Es measured on LP-CVD ZnO B films deposited at 155° C and 0.5mbar and with various doping levels, in function of the carrier density N. The dashed line and the full line are the predicted variations of Eg taking into account the Burstein-Moss effect alone, and both the Burstein-Moss and the band gap narrowing effects, respectively. Eo is the band gap of undoped ZnO and is set for the evaluation here to 3.3 eV. Reprinted with permission from [33]...

According to the Burstein-Moss effect [106,107], the optical band gap increases with carrier concentration n. This effect can be observed at the short wavelength turn-on of transmission. Between 400 and 600 nm all films show very high transmission of similar values above 82% in average. The differences above 600 nm can be attributed to free carrier absorption, resulting in lower transmission for highly doped films [108]. 

As the treated ITO samples show comparably high effective band gaps, we draw a conclusion as the following. A combination of Burstein-Moss-Shift and contributions of scattering [11] causes the increased Eg. It is not only a reason of Burstein-Moss-Shifl like Bender et al mentioned [13]. Eg = Eg q + AEg = Eg o + "R (37t nJ + fiZ, Where Eg... 

The optical properties were further studied by Nishino et al. [217], and Hu and Gordon [209, 210, 240], They observed an increase in the optical band gap (3.3-3.7 eV) with increasing doping, which can be explained again by the Burstein-Moss shift [128, 129]. The refractive index of ZnO films was in the range of 1.54-2.02 [234]. 

It is observed that the carrier concentration and mobility increased with H+ fluences. The increase in carrier concentration enhances the optical band gap of the as-implanted and post-annealed films as evident from the optical measuranents. The increase in band gap is attributed to the Burstein-Moss effect (White et al. 1979, Gritsyna and Kobyakov 1985) as given by the following formula ... 

Instead of the factor E + Et, - AkuT an alternative is to use the Burstein-Moss s... 

Results connected with practical implementation of the devices and improvements of the theoretical model were published by Ashley, Elliott, and White [332, 357]. They also described a stracture utilizing an opaque mask and lateral electrodes for signal readout to additionally eliminate noise somces. In 1990 a vertical exclusion photodetector with a self-filtering layer was proposed utilizing the Burstein-Moss effect in an n v structure to improve quantum efficiency [358],... 

Figure 3.6b shows a modification of this structure, a vertical exclusion photoconductor. In this case infrared radiation passes through an n" layer that at the same time serves as a passive Burstein-Moss filter in a manner also proposed for conventional cooled InSb photodiodes [359]. The main advantage of this stmcture is a higher ratio of the active area to the area where surface recombination appears, so that the relative portion of noise due to surface states to the total noise of the device is significantly reduced. 

ESR of pristine ZnO nanoparticles in vacuum before and after UV illumination and subsequently after exposure to air. Change in resistance to Ohmic behavior for a ZnO/PEDOT PSS junction upon UV exposure. Burstein-Moss effect (blue shift) occurs upon UV illumination by emptying the valence band and filling the conduction band. Adapted with permission from ref. 104. Copyright 2007, AIP Publishing EEC. Adapted with permission from ref. 105. Copyright (2010) American Chemical Society. 

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