Determination of a-Si:H Film Quality Throughfst and Sclc Techniques

1990 ◽  
Vol 192 ◽  
Author(s):  
R. Martins ◽  
M. Vieira ◽  
E. Fortunato ◽  
I. Ferreira ◽  
F. Soares ◽  
...  
Keyword(s):  
Diffusion Length ◽  
Surface Effect ◽  
Schottky Diodes ◽  
Effective Diffusion ◽  
Effective Lifetime ◽  
Thermally Activated ◽  
Best Parameter ◽  
And Diffusion ◽  
High Photosensitivity

ABSTRACTThe ambipolar diffusion length (L*) and the effective lifetime (τ*) in undoped a-Si:H films have been measured by the Flying Spot Technique (FST). This technique consists in measuring the decay range of charges in Schottky barriers and the potential induced by a laser beam with a constant motion rate. The data show that the FST measurements are quite suitable to determine separately the effective diffusion length and the effective lifetime of the carriers, taking into account the surface effect. The results also indicate that the photosensitivity is not the best parameter to characterize film quality. Indeed, films with high photosensitivity can present a poor lifetime and diffusion length that make them unsuitable to be used in optoelectronic devices. The results obtained by FST have been correlated with the Density of States (DOS) inferred by the Space Charge Limited Current (SCLC) measurements performed in the temperature range of 300–430 K and by the Constant Photocurrent Method (CPM) in forward biased Schottky diodes at room temperature. The dependence of the DOS on temperature shows that the SCLC technique is clearly influenced by the thermally activated carriers.

A-Si:H Ambipolar Diffusion Length and Effective Lifetime Measured by Flying Spot Technique (FST)

1991 ◽  
Vol 219 ◽  
Author(s):  
M. Vieira ◽  
R. Martins ◽  
E. Fortunato ◽  
F. Soares ◽  
L. Guimaraes
Keyword(s):  
Laser Beam ◽  
Transient Analysis ◽  
Diffusion Length ◽  
Transport Equations ◽  
Ambipolar Diffusion ◽  
Schottky Barriers ◽  
Effective Lifetime ◽  
Asymmetrical Distribution ◽  
Flying Spot

ABSTRACTThe determination of the ambipolar diffusion length, L*, and the effective lifetime, τ*, in p/i and a-Si:H Schottky barriers (ITO/p/a-Si:H/Al-Si; Cr/a-Si:H/Cr/Ag) have been determined by Flying Spot Technique, FST. This technique consists in the transient analysis of the photocurrent/photopotential induced by a laser beam that moves perpendicularly to the structure with a constant motion ratio, at different velocities. Taking into account the competition between the diffusion/drift velocities of the excess carriers and the velocity of the flying spot, it is possible to solve the transport equations and to compute separately L* and τ*, from the asymmetrical distribution responses.

Determination of the effective diffusion length of silicon solar cells from photoluminescence

2009 ◽  
Vol 105 (10) ◽  
pp. 104516 ◽  
Author(s):  
David Hinken ◽  
Karsten Bothe ◽  
Klaus Ramspeck ◽  
Sandra Herlufsen ◽  
Rolf Brendel
Keyword(s):  
Solar Cells ◽  
Diffusion Length ◽  
Effective Diffusion ◽  
Silicon Solar Cells

Determination of carrier lifetime and diffusion length in Al-doped 4H–SiC epilayers by time-resolved optical techniques

2014 ◽  
Vol 48 (2) ◽  
pp. 025103 ◽  
Author(s):  
Gediminas Liaugaudas ◽  
Donatas Dargis ◽  
Pawel Kwasnicki ◽  
Roxana Arvinte ◽  
Marcin Zielinski ◽  
...  
Keyword(s):  
Carrier Lifetime ◽  
Diffusion Length ◽  
Optical Techniques ◽  
Time Resolved ◽  
And Diffusion

Surface recombination effects on minority carrier diffusion length measurements using electron beam-induced current

1990 ◽  
Vol 48 (4) ◽  
pp. 744-745
Author(s):  
D.P. Malta ◽  
M.L. Timmons
Keyword(s):  
Electron Beam ◽  
Beam Energy ◽  
Minority Carrier ◽  
Diffusion Length ◽  
Effective Diffusion ◽  
Surface Recombination ◽  
Surface Recombination Velocity ◽  
Logarithmic Scale ◽  
Minority Carrier Diffusion Length ◽  
Carrier Diffusion

Measurement of the minority carrier diffusion length (L) can be performed by measurement of the rate of decay of excess minority carriers with the distance (x) of an electron beam excitation source from a p-n junction or Schottky barrier junction perpendicular to the surface in an SEM. In an ideal case, the decay is exponential according to the equation, I = Ioexp(−x/L), where I is the current measured at x and Io is the maximum current measured at x=0. L can be obtained from the slope of the straight line when plotted on a semi-logarithmic scale. In reality, carriers recombine not only in the bulk but at the surface as well. The result is a non-exponential decay or a sublinear semi-logarithmic plot. The effective diffusion length (Leff) measured is shorter than the actual value. Some improvement in accuracy can be obtained by increasing the beam-energy, thereby increasing the penetration depth and reducing the percentage of carriers reaching the surface. For materials known to have a high surface recombination velocity s (cm/sec) such as GaAs and its alloys, increasing the beam energy is insufficient. Furthermore, one may find an upper limit on beam energy as the diameter of the signal generation volume approaches the device dimensions.

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