Bandgap temperature dependence

Temperature-dependent luminescence measurements in the range from 77 to 300 K show quenching of the peak luminescence by a factor of about 15. Similar behavior is observed in the lifetime quenching [665, 666], As the band gap of the PECVD a-Si H is about 1.6 eV, nonradiative deexcitation of Er may occur at elevated temperatures. The amount of quenching lies in between that of c-Si and LPCVD a-Si H, just like the bandgap. 

Osuji C, Chao CY, Bita 1, Ober CK, Thomas EL. Temperature-dependent photonic bandgap in a self-assembled hydrogen bonded liquid-crystalline block copolymer. Adv Funct Mater... 

The bandgap varies depending on the polytype between 2.39 eV for 3C-SiC to 3.33 eV for 2H-SiC [2]. The most commonly nsed polytype is 4H-SiC, which has a band-gap of 3.265 eV [2]. The wide bandgap makes it possible to use SiC for very high-temperature operation. Thermal ionization of electrons from the valence band to the conduction band, which is the primary limitation of Si-based devices dnring high-temperature operation, is not a problem for SiC-based devices because of this wide bandgap. 

Fig. 10.5 Experimentally measured values of bandgap of PbSe films (horizontal bars The length gives the experimental uncertainty in size, mainly due to the size distribution). The broken curve gives the theoretical relationship between bandgap and crystal size based on the hyperbohc band approximation used for PbS in Ref. 40. The room-temperature reduced effective mass (0.034) was calculated from the low-temperature value (0.022) (R. Dalven, Infrared Phys. 9 141, 1969.) according to the temperature dependence given in H. Preier, Appl. Phys. 20 189, 1979. The dotted curve is a more recent calculation based on an envelope function calculation [41].

The second study of possible relevance reported that PbSe, precipitated from selenosulphate solution (not in the form of a film), was found to have an (electrical) bandgap, measured by temperature-dependent resistivity, of 0.4 eV [48], In the same study, samples prepared by reaction of solid lead tartrate with H2Se exhibited an electrical bandgap of 0.92 eV. These results suggest the occurrence of size quantization. 

FIGURE 1 Temperature dependence of bandgap change in various compound semiconductors [14],... 

The preceding bandgap values are given for low (2 - 10 K) temperature (T). Of primary importance is the temperature dependence of the bandgaps, in particular their value at room temperature (RT). From the previous discussion, different T dependencies are expected, due to the different strain state of the samples studied. For GaN on sapphire, both the residual epitaxial strain and the thermoelastic strain are compressive, whereas for GaN on SiC, the thermoelastic part of the residual strain is tensile. This leads to very different temperature dependencies between low T and RT, as shown in FIGURE 1. Note that results different from those shown on FIGURE 1 have also been reported [8],... 

Figure . Temperature dependences, for the passivated sample, of (a) positions of the NP and TO components of the A dot emission and corresponding quadratic fits. The behavior of the Si bandgap is shown for comparison (b) difference between the fitted curves for both components (c) intensity ratio of the TO and NP components.

The contributions of the generation current and the diffusion current, respectively, can be seperated by means of their temperature dependence. As iGen ia.exp f- Eg/2kT (Eg = Energy of bandgap) and Ioif exp - Eg/ kT, the diffusion current distribution is predominant at elevated temperatures (>j.60°C).In... 

The temperature dependence of the electron concentration in an intrinsic oxide semiconductor depends on the equilibrium constant for thermal generation of electrons and electron holes and on the bandgap Eg. What is this relationship ... 

Fig. 27.11 Temperature dependence of a the Young s modulus [7] and b the Raman shifts at the atmospheric pressure for ZnO with confirmation of = 310 K and derivative of = 0.75 eV per bond, which is in accordance with that derived from T-dependent bandgap change (inset b [111-114]) of ZnO [19]. Pressure dependence of c elastic modulus [115] and d optical modes [Ei(LO), E2(high), Ei(TO), Ai(TO), and Bi(LO)] for ZnO [109, 110] with derivative of the binding energy density (Ej) of 0.097 eV/A (reprinted with permission from [19])...

These lifetimes are extremely short because there are so many majority carriers to combine with. Neither the diffusion coefficients nor the lifetimes are particularly temperature dependent, but nf exp -Eg/kT). The leakage current can be minimized by selecting a high bandgap material and by heavy doping. Typical values for the leakage current density Jo are 0(10 A/m ) at ambient temperatures. 

---