Space charge limited density

Let us calculate the space-charge-limited density of proton current I p(S ) needed for this purpose is obtained from the right-hand side of formula (222) divided by enS. Putting en from Eq. (224) into Eq. (225), we arrive at the differential equation... 

The hole current in this LED is space charge limited and the electron current is contact limited. There are many more holes than electrons in the device and all of the injected electrons recombine in the device. The measured external quantum efficiency of the device is about 0.5% al a current density of 0.1 A/cm. The recombination current calculated from the device model is in reasonable agreement with the observed quantum efficiency. The quantum efficiency of this device is limited by the asymmetric charge injection. Most of the injected holes traverse the structure without recombining because there are few electrons available to form excilons. 

Fig. 8 Temperature dependence of the zero field hole mobility in the low carrier density limit in a polyfluorene copolymer. The data are inferred from space-charge-limited current experiments and analyzed in terms of the extended Gaussian disorder model (see Sect. 4.1). From [90] with permission. Copyright (2008) by the American Institute of Physics...

The work of Mensfoort et al. is a striking test of the importance of charge carrier density effects in space-charge-limited transport studies. For a given applied voltage the space charge concentration is inversely proportional to the device thickness. This explains why in Fig. 9 the deviation from the In cx... 

Fig. 13 Experimental (symbols) and theoretical (lines) data for the current-density as a function of applied voltage for a polymer film of a derivative of PPV under the condition of space-charge-limited current flow. Full curves are the solution of a transport equation that includes DOS filling (see text), dashed lines show the prediction of Child s law for space-charge-limited current flow assuming a constant charge carrier mobility. From [96] with permission. Copyright (2005) by the American Institute of Physics...

Space-Charge-Limited Diode. This method is equally applicable to electropositive and electronegative adsorbed layers. In a diode the maximum current which can be drawn from the cathode is given by the emission formula in Sec. V,A. Electrons emitted from the cathode at low current densities build up an electron atmosphere or space charge at the surface, and this space charge presents an electrostatic barrier to electrons flowing to... 

Steady-state space charge limited currents (SCLC) have been applied to study traps in organic solids since the early 1960 s (Mark and Helfrich, 1962 Thomas et al., 1968 Reucroft and Mullins, 1974). Superquadratic dependences of the currents upon voltage, J azVn where n > 2, have been interpreted assuming the presence of traps exponentially distributed over a wide energy range. This may be expressed by (20), where h(e) is the density of states per... 

Support for the applicability of this model to an explanation of the Meyer-Neldel rule comes from measurements of space-charge limited currents in anthracene where a correlation (see Fig. 20) has been found between the total density of traps H and the distribution parameter Tc (Owen et al, 1974). It has been shown that this effect is not fortuitous as suggested by some workers... 

We begin by assuming that the ion current density to all internal surfaces is equal. Then, if we assume a collision-free sheath with the field being zero at the edge of the positive column, we can express the space charge-limited ion current as16... 

Fig. 4.20. The density of states distribution obtained from space charge limited current measurements on undoped a-Si H. The various symbols represent different samples and deposition conditions. Field efiect (FE) and DLTS data are shown for comparison. is the substrate temperature during growth (Mackenzie, LeComber and Spear 1982).

The observation of space charge limited currents (SCLC) in nanoscaled pure and chromium-doped titania was reported [310] and both the free-charge carrier density and the trapped-charge carrier density were given. 

It should be emphasized that a carrier transport can only be described by Ohm s law (Eq. 1.35) if sufficient empty energy levels exist in the corresponding energy band and a minimum carrier density is present in the material. On the other hand, in the case of an intrinsic high bandgap semiconductor, the carrier density may be negligible so that only those carriers carry the current which are injected into the crystal via one contact. In this case we have a space charge limited current which is proportional to (Child s law). 

The IV behaviour is described with a formation of a space charge upon the dominant electron-injection (space charge limited currents, SCLC). The current density follows a power law dependence, described with the Mott-Goumier formula in (1)... 

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