Effect of Fermi Level Pinning at the Surface During OMVPE Growth

AbstractDuring organometallic vapor phase epitaxy of GaAs, the Fermi energy is found to be pinned ≈200 meV below the intrinsic Fermi energy on a (lOO)-oriented surface. This was determined by making the first comparison of Zn concentration, Nzn. obtained from growth with that obtained at equilibrium, all under the same nominal ambient conditions. Donor solubility has been found to be virtually unchanged during growth of n- or p-type GaAs, and this is strong evidence that the Fermi level remains pinned at essentially the same energy during growth of n- or p-type GaAs. Consistent with Fermi level pinning, we find (1) the NZn is supersaturated in the epilayer for the ambient growth conditions used, (2) a large excess concentration of positively charged Ga interstitials can be grown into n-type GaAs and which diffuses into nearby p-type layers, causing (3) the Zn diffusivity, DZn ∼10−13 cm2/s, out of buried npn layers to be essentially independent of the ambient conditions. Annealing of a heavily Zn-doped layer at the surface can lead to 10−16<DZn<10−13 cm2/s at T=800°C simply by varying the Zn partial pressure over its commonly used range. Use of In-doped spikes in n- and p-type GaAs suggest that interstitial point defects have a strong effect on the group III diffusion.

Download Full-text

Fermi-Level effect and junction carrier concentration effect on p-Type dopant distribution in IlI-V Compound superlattices

MRS Proceedings ◽

10.1557/proc-535-219 ◽

1998 ◽

Vol 535 ◽

Author(s):

Chang-Ho Chen ◽

Ulrich M. Gösele ◽

Teh Y. Tan

Keyword(s):

Electric Field ◽

Fermi Level ◽

Hole Concentration ◽

Equilibrium Concentration ◽

Dopant Atom ◽

Group Iii ◽

Atom Diffusion ◽

Segregation Phenomenon ◽

P Type ◽

Positively Charged

AbstractThe pronounced segregation phenomenon in the distribution of p-type dopants Zn and Be in GaAs and related III-V compound heterostructures has been explained quantitatively by treating simultaneously the processes of dopant atom diffusion, segregation, and the effect of heterojunction carrier concentrations on these two aspects. Segregation of a dopant species between two semiconductor heterostructure layers is described by a model incorporating (i) a chemical effect on the neutral species; and (ii) in addition, a Fermi-level effect on the ionized species. The process of Zn and Be diffusion in GaAs and related compounds is governed by the doubly-positively-charged group III element self-interstitials whose thermal equilibrium concentration and hence also the Zn and Be diffusivities exhibit also a Fermi-level dependence, i.e., in proportion to p2.A heterojunction is consisting of a space charge region with an electric field, in which the hole concentration is different from those in the bulk layers. This influences the junction region concentrations of and of Zn− or Be−, which in turn influence the distribution of the ionized acceptor atoms. The overall process involves diffusion and segregation of holes, , Zn− or Be−, and an ionized interstitial acceptor species. The junction electric field also changes with time and position.

Download Full-text

Are the Models of the Triply Charged Gallium Vacancy and Doubly Charged Gallium Interstitial Alive or Dead?

MRS Proceedings ◽

10.1557/proc-378-959 ◽

1995 ◽

Vol 378 ◽

Author(s):

R. M. Cohen ◽

C. Y. Chen ◽

W. M. Li ◽

D. S. Simons ◽

P. H. Chi

Keyword(s):

Negative Charge ◽

Growth Conditions ◽

Gallium Vacancy ◽

Group Iii ◽

Multiply Charged ◽

Diffusion Mechanisms ◽

P Type ◽

Doubly Charged ◽

Charged Defects ◽

Positively Charged

AbstractWe have found that the measured diffusivity can be quite different than predicted by recent models of multiply-charged defects. Key problems dealing with the measurement and the interpretation of diffusion mechanisms are discussed. Using a few common variations in GaAs epilayer growth, we have obtained diffusivities which range over several orders of magnitude at the same temperature. Making use of the relatively weak In-As bond, we have used In as a marker to measure group III interdiffusion, DIII. DIII is consistent with the results of others using Al as a marker in n-type GaAs, but orders of magnitude smaller than predicted by the triply charged Ga vacancy, V3−Ga, model of Tan and Gosele. Although diffusion can be attributed to a negatively charged vacancy in n-type GaAs, In is found to often move by a kick-out mechanism in p-type GaAs. It appears likely that many early experiments with n- and p-type GaAs-AlAs interdiffusion were affected by large concentrations of Ga interstitials, IGa, caused by Fermi energy pinning at the growing surface. We present the first direct experimental evidence for the existence of a positively charged Ga interstitial. Our results, combined with those of others, suggest that VGa has a single negative charge associated with it. Because epilayer growth conditions appear to cause the point defect concentrations to deviate substantially from equilibrium, we conclude that the exact charge states of VGa and IGa still remain to be determined.

Download Full-text

Anomalously persistent p-type behavior of WSe2 field-effect transistors by oxidized edge-induced Fermi-level pinning

Journal of Materials Chemistry C ◽

10.1039/d1tc04148g ◽

2022 ◽

Author(s):

Tien Dat Ngo ◽

Min Sup Choi ◽

Myeongjin Lee ◽

Fida Ali ◽

Won Jong Yoo

Keyword(s):

Fermi Level ◽

Field Effect ◽

Field Effect Transistors ◽

High Mobility ◽

Two Dimensional ◽

Edge Contact ◽

Fermi Level Pinning ◽

P Type

A technique to form the edge contact in two-dimensional (2D) based field-effect transistors (FETs) has been intensively studied for the purpose of achieving high mobility and also recently overcoming the...

Download Full-text

STM studies of Fermi-level pinning on the GaAs(001) surface

Philosophical Transactions of the Royal Society of London Series A Physical and Engineering Sciences ◽

10.1098/rsta.1993.0106 ◽

1993 ◽

Vol 344 (1673) ◽

pp. 533-543 ◽

Cited By ~ 3

Keyword(s):

Fermi Level ◽

Valence Band ◽

Surface Defects ◽

Defect Density ◽

Valence Band Maximum ◽

Intrinsic Defect ◽

Fermi Level Pinning ◽

Donor States ◽

P Type ◽

Surface Donor

This paper reviews recent scanning tunnelling microsopy (STM) studies of Fermi-level pinning on the surface of both n- and p-type GaAs(001). The samples are all grown by molecular beam epitaxy and have a (2 x 4)/c(2 x 8) surface reconstruction. The STM has shown that on the surface of highly doped n-type GaAs(001) there is a high density of kinks in the dimer-vacancy rows of the (2 x 4) reconstruction. These kinks are found to be surface acceptors with approximately one electron per kink. The kinks form in exactly the required number to pin the Fermi-level of n-type GaAs(001) at an acceptor level close to mid gap, irrespective of doping level. The Fermi-level position is confirmed with tunnelling spectroscopy. No similar surface donor states are found on p-type GaAs(001). In this case Fermi-level pinning results from ‘intrinsic’ surface defects such as step edges. Since this intrinsic defect density is independent of doping, at high doping levels the Fermi-level on p-type GaAs(001) moves down in the band gap towards the valence band. Tunnelling spectroscopy on p-type GaAs(001) doped 10 19 cm -3 with Be shows the Fermi-level to be 150 mV above the valence band maximum

Download Full-text

NEGATIVE MAGNETORESISTANCE IN PbTe(Mn,Cr)

International Journal of Modern Physics B ◽

10.1142/s0217979202014371 ◽

2002 ◽

Vol 16 (20n22) ◽

pp. 3343-3346 ◽

Cited By ~ 2

Author(s):

D. KHOKHLOV ◽

I. IVANCHIK ◽

A. KOZHANOV ◽

A. MOROZOV ◽

E. SLYNKO ◽

...

Keyword(s):

Fermi Level ◽

Band Edge ◽

Negative Magnetoresistance ◽

Conduction Band Edge ◽

Valence Band Edge ◽

Narrow Gap ◽

Magnetoresistance Effect ◽

Fermi Level Pinning ◽

P Type ◽

Substantial Drop

We have observed the negative magnetoresistance effect in the narrow-gap PbTe(Mn,Cr) semiconductor, in which the Fermi level is pinned within the gap nearby the conduction band edge. Previously the giant negative magentoresistance effect has been reported in PbTe(Mn,Yb), in which the Fermi level is pinned in the gap nearby the valence band edge. It is known that in the case of Yb doping the Fermi level pinning results from the 2+ - 3+ valence instability of an impurity. The same sort of the valence instability provides the Fermi level pinning in PbTe(Mn,Cr), but the conductivity is of the n-type, not of the p-type as in PbTe(Mn,Yb). Introduction of magnetic field leads to substantial drop of the PbTe(Mn,Cr) resistivity of about 30% at T = 4.2 K. This is however much lower than in PbTe(Mn,Yb), where the effect amplitude reached 3 orders of magnitude. The effect disappears at T = 15 K. Possible mechanisms of the effect are discussed.

Download Full-text

Fermi level pinning of p-type semiconducting indium phosphide contacting liquid electrolyte solutions: rationale for efficient photoelectrochemical energy conversion

Journal of the American Chemical Society ◽

10.1021/ja00395a065 ◽

1981 ◽

Vol 103 (5) ◽

pp. 1261-1263 ◽

Cited By ~ 25

Author(s):

Raymond N. Dominey ◽

Nathan S. Lewis ◽

Mark S. Wrighton

Keyword(s):

Indium Phosphide ◽

Fermi Level ◽

Energy Conversion ◽

Electrolyte Solutions ◽

Liquid Electrolyte ◽

Fermi Level Pinning ◽

P Type

Download Full-text

Decoupling the Fermi-level pinning effect and intrinsic limitations on p-type effective work function metal electrodes

Microelectronic Engineering ◽

10.1016/j.mee.2007.05.006 ◽

2008 ◽

Vol 85 (1) ◽

pp. 2-8 ◽

Cited By ~ 45

Author(s):

Huang-Chun Wen ◽

Prashant Majhi ◽

Kisik Choi ◽

C.S. Park ◽

Husam N. Alshareef ◽

...

Keyword(s):

Fermi Level ◽

Work Function ◽

Metal Electrodes ◽

Effective Work ◽

Effective Work Function ◽

Fermi Level Pinning ◽

Pinning Effect ◽

P Type

Download Full-text

Beam Annealing of Ion-Implanted Gaas and Inp

MRS Proceedings ◽

10.1557/proc-1-261 ◽

1980 ◽

Vol 1 ◽

Cited By ~ 3

Author(s):

J. C. C. Fan ◽

R. L. Chapman ◽

J. P. Donnelly ◽

G. W. Turner ◽

C. O. Bozler

Keyword(s):

Solar Cells ◽

Electrical Properties ◽

Ion Implantation ◽

Fermi Level ◽

Laser Annealing ◽

Electrical Activation ◽

Fermi Level Pinning ◽

P Type ◽

Conversion Efficiencies ◽

Ion Implanted

ABSTRACTA scanned cw Nd: YAG laser was used to anneal ion-implanted GaAs and InP wafers. Measurements show that electrical activation is greater for p-type than for n-type dopants in GaAs, while in InP, the opposite is observed. A simple Fermi-level pinning model is presented to explain not only the electrical properties we have measured, but also those observed by other workers. We have fabricated GaAs and InP solar cells with junctions formed by ion implantation followed by laser annealing. The GaAs cells have much better conversion efficiencies than the InP cells, and this difference can be explained in terms of the model.

Download Full-text

Contactless Electromodulation Characterization of Compound Semiconductor Surfaces and Device Structures

MRS Proceedings ◽

10.1557/proc-324-141 ◽

1993 ◽

Vol 324 ◽

Cited By ~ 3

Author(s):

J.M. Woodall

Keyword(s):

Fermi Level ◽

Electric Fields ◽

Growth Conditions ◽

Compound Semiconductor ◽

Conduction Band Edge ◽

Semiconductor Surfaces ◽

Air Exposure ◽

Fermi Level Pinning ◽

Characterization Of Properties

AbstractThis paper will review the use of contactless electromodulation methods, such as photoreflectance (PR) and contactless electroreflectance (CER), to characterize the electronic properties of compound semiconductor surfaces exposed to different growth and post-growth conditions. Also the characterization of properties critical to device performance can be evaluated. For example, using PR and CER it has been found that there is a lower density of surface hole traps than electron traps in certain as-grown MBE (001) GaAs samples and that this condition persists even after air exposure. This behaviour is in contrast to other samples, including both bulk and MBE grown (001) surfaces in which the Fermi level is pinned mid-gap for both n- and p-type structures. We also have observed that Ar+ bombardment under UHV conditions results in Fermi level pinning close to the conduction band edge and that thermal annealing restores mid-gap pinning. Finally, using PR we are able to characterize the electric fields and associated doping levels in the emitter and collector regions of heterojunction bipolar transistor structures (fabricated from III-V materials), thus demonstrating the ability to perform inprocess evaluation of important device parameters.

Download Full-text