214 CHAPTER 4. JUNCTIONS IN SEMICONDUCTORS:P-NDIODES
Problem 4.13We will define ap-ndiode to be “turned on” when the current density
reaches 103 A/cm^2 (this is an approximate criterion). Calculate the turn-on orcut-in
voltage for a GaAs and a Sip-ndiode with following parameters (same for both diodes):
Nd = Na=10^17 cm−^3
τn = τp=10−^8 s
Use table 3.1 to determine diffusion coefficients. Assume that the diodes are long andT=
300 K.
Problem 4.14An important use of a forward-biasedp-ndiode is as an emitter in a bipolar
transistor. In the emitter it is desirable that the current be injected via only one kind of
charge. The diode efficiency is thus defined as (Jnis the current density carried by
electron injection into thep-side)
γinj=
Jn
JTot
=
1
1+Jp/Jn
Consider a GaAsp-ndiode with the following parameters:
Electron diffusion coefficient, Dn =30cm^2 /s
Hole diffusion coefficient, Dp =15cm^2 /s
p-side doping, Na =5× 1016 cm−^3
n-side doping, Nd =5× 1017 cm−^3
Electron minority carrier time, τn =10−^8 s
Hole minority carrier time, τp =10−^7 s
Calculate the diode injection efficiency (this is called the emitter efficiency in a bipolar
transistor).
Problem 4.15Consider thep-ndiode in problem 4.12. In that problem we examined the
prefactor of the diode current using the long diode conditions. Calculate the prefactor for
the case of a short diode in which both then-andp-side widths are 5.0μm.
4.12FURTHERREADING ...............................
- General
- M. S. Tyagi,IntroductiontoSemiconductorMaterialsandDevices (John Wiley and
Sons, New York, 1991).
- B. G. Streetman and S. Banerjee,SolidStateElectronicDevices (Prentice-Hall, En-
glewood Cliffs, NJ, 1999).
- G. W. Neudeck, “Modular Series on Solid State Devices,” Vol. 11,TheP-NJunction
Diode, (Addison-Wesley, Reading, MA, 1983).
