An Assessment of the Light Modulated Photocurrent Method in the Study of the Density of Gap States in Hydrogenated Amorphous Silicon

ABSTRACTWe have applied the modulated photocurrent (MPC) method over a wide range of frequencies (5Hz-100kHz) and temperatures (120K-380K) to assess its ability to accurately deduce the mobility gap distribution in a-Si:H. We have also investigated the effects of moving both the Fermi level within some samples (by light soaking and partial annealing) and the quasi-Fermi level (by applying the bias light) to observe how such changes influence the deduced density of states (DOS). We then compared the MPC results directly with the DOS determined by junction capacitance measurements in the same sample devices. We have determined general conditions under which, we believe, the MPC results provide an accurate picture of the gap state distribution. However, we found that under other conditions, the appearance of the deep defect peaks and other features do not represent the actual defect distribution but, rather, are artifacts due to recombination processes.

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Gap state distribution and Fermi level pinning in monolayer to multilayer MoS2 field effect transistors

Nanoscale ◽

10.1039/d0nr01379j ◽

2020 ◽

Vol 12 (16) ◽

pp. 8883-8889 ◽

Cited By ~ 5

Author(s):

Ronen Dagan ◽

Yonatan Vaknin ◽

Yossi Rosenwaks

Keyword(s):

Transition Metal ◽

Fermi Level ◽

Field Effect ◽

Field Effect Transistors ◽

High Surface ◽

Volume Ratio ◽

Transition Metal Dichalcogenide ◽

State Distribution ◽

Fermi Level Pinning ◽

Gap States

Gap states and Fermi level pinning play an important role in all semiconductor devices, but even more in transition metal dichalcogenide-based devices due to their high surface to volume ratio and the absence of intralayer dangling bonds.

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Probing the Densities of Gap States in Intrinsic a-Si:H Using Space Charge Limited Currents of Electrons and Holes

MRS Proceedings ◽

10.1557/proc-192-145 ◽

1990 ◽

Vol 192 ◽

Cited By ~ 3

Author(s):

Robin M. Dawson ◽

J. H. Smith ◽

C. R. Wronski

Keyword(s):

Space Charge ◽

Density Of States ◽

Carrier Transport ◽

Hydrogenated Amorphous Silicon ◽

Wide Range ◽

Self Consistent ◽

Gap States ◽

Hydrogenated Amorphous ◽

Space Charge Limited Currents ◽

Space Charge Limited

ABSTRACTSpace charge limited currents of holes in intrinsic hydrogenated amorphous silicon (a-Si:H) have been obtained using novel p+-intrinsic-p+ (p-i-p) structures. The presence of these hole space charge limited currents is verified from their temperature dependence and their dependence on a wide range of intrinsic layer thickness. The carrier transport and space charge limited currents in the p-i-p structures are compared with those of n-i-n structures and the results are discussed in terms of a self consistent density of states in the gap.

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Toward a Practical Model of a-Si:H Defects in Intensity-Time-Temperature Space

MRS Proceedings ◽

10.1557/proc-336-165 ◽

1994 ◽

Vol 336 ◽

Cited By ~ 7

Author(s):

D. Caputo ◽

J. Bullock ◽

H. Gleskova ◽

S. Wagner

Keyword(s):

Light Intensity ◽

Fermi Level ◽

Amorphous Silicon ◽

Thermal Annealing ◽

Hydrogenated Amorphous Silicon ◽

Defect States ◽

Quasi Fermi Level ◽

Practical Model ◽

Density Of Defect States ◽

Hydrogenated Amorphous

ABSTRACTIn this paper we develop a model of the defect kinetics in hydrogenated Amorphous silicon (a:Si:H) with the goal of predicting the density of defect states g (E) established by any given light intensity I, for arbitrary times t and temperatures T. While we build on widely accepted expressions for the the rates of light-induced and thermal annealing, we examine in more detail the light induced annealing (LIA) term. The model shows that the LIA process can be described with the thermal annealing term if a suitable reduction to the annealing energy is introduced. This reduction depends on the light intensity such as to suggest a relation to the shift of the electron quasi-Fermi level under illumination.

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Charged Defect State Distributions Obtained from the Analysis of Photoconductivities in Intrinsic a-Si:H Films

MRS Proceedings ◽

10.1557/proc-336-413 ◽

1994 ◽

Vol 336 ◽

Cited By ~ 6

Author(s):

Mehmet Güneş ◽

R. W. Collins ◽

C. R. Wronski

Keyword(s):

Charged Defect ◽

Defect States ◽

State Distribution ◽

Spin Resonance ◽

Neutral Defect ◽

Gap States ◽

Hydrogenated Amorphous ◽

Defect Densities ◽

Positively Charged ◽

Spin Densities

ABSTRACTSteady-state photoconductivity, sub-bandgap absorption and electron spin resonance (ESR) Measurements were carried out on annealed and light soaked intrinsic hydrogenated Amorphous silicon (a-Si:H) films. The experimental results were modeled using detailed numerical Model. The defect densities derived from the sub-bandgap absorption in the light soaked films were correlated with the ESR spin densities. Selfconsistent fitting of the data was obtained using a gap state distribution which consists of positively charged defect states above, negatively charged defect states below and neutral defect states at about Midgap. Both the annealed and the light degraded states are modeled using the same distribution of gap states whose densities increase upon light soaking with a slight increase in the ratio of the neutral to charged defect densities. These results on intrinsic a-Si:H are consistent with those of charged defect Models.

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Role of the Fermi level in the formation of electronic band-tails and mid-gap states of hydrogenated amorphous silicon in thin-film solar cells

Journal of Applied Physics ◽

10.1063/1.4989425 ◽

2017 ◽

Vol 122 (9) ◽

pp. 093101 ◽

Cited By ~ 2

Author(s):

A. Bidiville ◽

T. Matsui ◽

H. Sai ◽

K. Matsubara

Keyword(s):

Thin Film ◽

Solar Cells ◽

Fermi Level ◽

Amorphous Silicon ◽

Hydrogenated Amorphous Silicon ◽

Thin Film Solar Cells ◽

Electronic Band ◽

Gap States ◽

Hydrogenated Amorphous

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RECOMBINATION PROCESSES AND GAP STATES IN HYDROGENATED AMORPHOUS SILICON AS ELUCIDATED BY TIME-RESOLVED LUMINESCENCE MEASUREMENTS

Le Journal de Physique Colloques ◽

10.1051/jphyscol:19814128 ◽

1981 ◽

Vol 42 (C4) ◽

pp. C4-587-C4-590

Author(s):

I. Hirabayashi ◽

K. Morigaki ◽

S. Nitta

Keyword(s):

Amorphous Silicon ◽

Hydrogenated Amorphous Silicon ◽

Time Resolved ◽

Recombination Processes ◽

Gap States ◽

Hydrogenated Amorphous

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Magnetic Resonance Probes Of Band Tail States And Defects In Tetrahedrally Coordinated Amorphous Semiconductors

MRS Proceedings ◽

10.1557/proc-715-a2.3 ◽

2002 ◽

Vol 715 ◽

Cited By ~ 2

Author(s):

P. C. Taylor

Keyword(s):

Amorphous Silicon ◽

Hydrogenated Amorphous Silicon ◽

Amorphous Semiconductors ◽

Dangling Bonds ◽

Band Tail ◽

Wide Range ◽

Recombination Processes ◽

Staebler Wronski Effect ◽

Hydrogenated Amorphous ◽

Kinetics Of

AbstractRecent electron spin resonance (ESR) results relating to (1) recombination processes for optically excited electrons and holes in tetrahedrally coordinated amorphous semiconductors and (2) kinetics of metastable defects (dangling bonds associated with the Staebler-Wronski effect) in hydrogenated amorphous silicon (a-Si:H). With regard to recombination processes, ESR measurements have been performed over a wide range of excitation intensities (nW/cm2 to W/cm2) on hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous germanium (a-Ge:H). The kinetics can be studied down to carrier densities as low as 1014 cm-3. The longtime decay curves show that at large carrier separation (1) the random distribution of optically excited electrons and holes is subject to the condition of charge neutrality, and (2) the decays are universal and independent of the densities of localized, band-tail states. With regard to the metastable defects in a-Si:H, the kinetics of the production and thermal annealing of silicon dangling bonds have been measured at temperatures between 25 and 480 K using ESR. Below about 150 K the measurement of the dangling bonds is masked by long-lived, band tail carriers that accumulate with time. The production rate for silicon dangling bonds decreases with decreasing temperature and is nearly temperature independent below approximately 100 K. Defects created by 10 hours of irradiation below 100 K anneal almost completely at 300 K. In a- Ge:H, the first measurements of optically induced, metastable germanium dangling bonds have been made.

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Polymorphous Silicon: Transport Properties and Solar Cell Applications

MRS Proceedings ◽

10.1557/proc-557-501 ◽

1999 ◽

Vol 557 ◽

Cited By ~ 21

Author(s):

C. Longeaud ◽

J. P. Kleider ◽

M. Gauthier ◽

R. Brtiggemann ◽

Y. Poissant ◽

...

Keyword(s):

Fermi Level ◽

Transport Properties ◽

Density Of States ◽

Diffusion Length ◽

Hydrogenated Amorphous Silicon ◽

Capacitance Measurements ◽

New Material ◽

Hydrogenated Amorphous ◽

Minority Carriers ◽

Excellent Stability

AbstractTransport properties of hydrogenated polymorphous silicon layers (pm-Si:H) deposited at 150°C under various pressures in the range 80-293 Pa in sandwich (Schottky and p-i-n diodes) and coplanar structures have been compared to those of hydrogenated amorphous silicon (a-Si:H) samples deposited at the same temperature in standard conditions. The layers have been studied as-deposited, annealed and after light-soaking. With increasing pressure up to 240 Pa: i) the density of states above the Fermi level decreases as determined by means of the modulated photocurrent technique, ii) the mobility-lifetime products of electrons and holes measured by means of steady-state photoconductivity and photocarrier grating techniques both increase. The highest values for the diffusion length of minority carriers exceed 200 nm. Capacitance measurements as a function of frequency and temperature show that the density of states at the Fermi level is lower in the pm-Si:H than in the a-Si:H films. After light-soaking the diffusion length of minority carriers in a-Si:H is reduced by a factor oftwo whereas it is less reduced or not affected in the pm-Si:H layers. Solar cells including this new material present an excellent stability.

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