Space charge limited diode

The C.P.D. is obtained directly by the magnetron and the capacitor (or Kelvin) methods. Other methods which have proved successful rely on the variation of anode potential in a diode with constant cathode conditions. In this case, since adsorption changes the effective anode potential, the applied potential necessary to restore the anode current to its original value is equal to the C.P.D. between the two surfaces. As considered in Sec. II, a true average work function is measured in the C.P.D. method when the two conductors are separated by a distance which is much greater than the size of the patches on the surface. These conditions are invariably fulfilled in the capacitor and the space-charge-limited diode methods. 

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... 

Fig. 15. Current-voltage curves obtained in the space-charge-limited diode.

Fig. 13. Electrode assemblies for the determination of work functions with the space charge limited diode (a) crossed filaments (b) filament cathode, evaporated metal film anode. ...

Fig. 27 Compositional dependence of electron and hole mobilities in MDMO-PPV PCBM blend films as obtained by space charge limited diode currents. Clearly the mobility for holes is increased upon addition of the fullerene. (Reproduced from [144] with permission, 2005, Wiley-VCH)...

A. Van der Ziel, Space-Charge-Limited Solid-State Diodes... 

A.J. Campbell, D.D.C. Bradley, H. Antoniadis, M. Inbasekaran, W.W. Wu, and A.P. Woo, Transient and steady-state space-charge-limited currents in polyfluorene copolymer diode structures with ohmic hole injection contacts, Appl. Phys. Lett., 76 1734-1736, 2000. 

N. Holonyak, Jr. and M. H. Lee, Photopumped III-V Semiconductor Lasers H. Kressel and J. K Butler, Heterojunction Laser Diodes A Van der Ziel, Space-Charge-Limited Solid-State Diodes P. J. Price, Monte Carlo Calculation of Electron Transport in Solids... 

Wolf U, Barth S, Bassler H (1999) Electrode versus space-charge-limited conduction in organic light-emitting diodes. Appl Phys Lett 75 2035... 

M. Koehler, L.S. Roman, O. Inganas, M.G.A. da Luz Space-charge-limited bipolar currents in polymer/Ceo diodes, J. Appl. Phys. 92, 5575 (2002)... 

A. Van der Ziel, Space-Charge-Limited Solid-State Diodes P J. Price, Monte Carlo Calculation of Electron Transport in Solids... 

FIGURE 8.18 Typical I—E curve for a hole-only diode exhibiting space charge-limited behavior. The gray line has a slope of 2 on the log-log scale and is meant as a guide to the eye. 

Numerically, the matrix sheath thickness is large and exceeds the Debye radius by 10-50 times at high voltages. A more accmate approach, the so-called Child law sheath, takes into account a decrease in the ion density due to their acceleration across the sheath. In frameworks of the model, the ion current density Jq = n eu is taken from the Child law of space-charge-limited current in a plane diode ... 

---