A survey of ohmic contacts to iiiv compound semiconductors. How i tricked my brain to like doing hard things dopamine detox duration. Fermi level depinning and contact resistivity reduction using a reduced titania interlayer in nsilicon metalinsulatorsemiconductor ohmic contacts ashish agrawal,1 joyce lin,2 michael barth,1 ryan white,3 bo zheng,4 saurabh chopra,4 shashank gupta,4 ke wang,1 jerry gelatos,4 suzanne e. Suppose nd or na in the semiconductor is very large. As you can see from the figure 2a, applying a positive bias to the metal makes electrons to flow easily downhill, while negative bias makes the flow from the metal part to the semiconductor and this the picture of an ohmic contact. Pdf ohmic contacts for high power and high temperature. Fermi level depinning and contact resistivity reduction. Metalsemiconductor contacts fermi level pinning is the lack of barrier height modulation with metal work function due to either large density of intrinsic states.
Both ohmic contacts and schottky barriers are dependent on the schottky barrier height, which sets the threshold for the excess energy an electron requires to pass from the semiconductor to the metal. Effect is different in inas as any metal becomes ohmic. The term metalsilicon contact includes silicidesi contacts. An ohmic contact to a semiconductor layer including a heterostructure barrier layer and a metal layer adjacent to the heterostructure barrier layer is provided. Sma5111 compound semiconductors lecture 2 metal semiconductor junctions outline introduction structure what are we talking about. Ga 2 o 3 layer that can be mildly ndoped or even undoped.
It is claimed that schottky type of contact between low work function ptype semiconductor and higher work function metal creates an ohmic contact in which current can flow both sides almost fluently with very low resistance. Metalsemiconductor junction an overview sciencedirect. Then the depletion region width at the metal semiconductor interface xd 2 k. Semiconductor contacts physics of semiconductor devices wiley online library. Importance of metalsemiconductor contacts is due to 1 ohmic metalsemiconductor junctions e. Schottky barrier diodes sufficiently that it is widely used.
When a metal and semiconductor are brought into contact, there are two types of junctions formed depending on the work function of the. For example, good ohmic contacts are essential for achieving excellent electrical characteristics of a semiconductor device, while schottky i. An ideal ohmic contact, a contact in which no potential exists between the metal and the semiconductor, is made to the other side of the semiconductor. Metalsemiconductors contacts engineering libretexts. Ee311 saraswat ohmic contacts 5 for a tunneling contact the net semiconductor to metal current is given by jsm at k. For a sufficiently large schottky barrier height, where. Metal semiconductor interfaces rectifying schottky junction nonrectifying ohmic contacts 3. Schottky barrier determined by surface states rather than metal and semiconductor workfunction difference. An ideal ohmic contact is a low resistance, and nonrectifying junction with no potential exists between the the metalsemiconductor interface.
Sma5111 compound semiconductors lecture 2 metalsemiconductor junctions outline introduction structure what are we talking about. The sign convention of the applied voltage and current is also shown in figure 1. The small barrier that exists for electron flow from metal to the semiconductor, but vanishes when. Ohmic, rectifying, neither band picture in thermal equilibrium establishing the baseline ideal junction no surface states real junctions surface states and fermi level pinning applying voltage bias iv and cv where it gets. A survey of ohmic contacts to iiiv compound semiconductors a. Metalsemiconductor ohmic contacts stanford university. Whenever a metal and a semiconductor are in intimate contact, there exists a potential barrier between the two that prevents most charge carriers electrons or holes from passing from one to the other only a small number of carriers have enough energy to get. It is also claimed that electrons have tendency to flow when no potent. Metalsemiconductor ohmic and schottky contacts byu. An ohmic contact between a metal and a semiconductor is defined as one with a negligibly small impedance compared to the series impedance of the bulk of the semiconductor. An ideal ohmic contact is a low resistance, and nonrectifying junction with no potential exists between the the metal semiconductor interface. The term metal silicon contact includes silicidesi contacts.
Metal semiconductor interfaces rectifying schottky junction nonrectifying ohmic contacts 4. It consists of a metal contacting a semiconductor surface, or junction. Conduction mechanisms for metalnsemiconductor contacts as a function of the barrier height and width. In a normal pn junction diode, a ptype semiconductor and an ntype semiconductor are used to form the pn junction. The rectifying schottky characteristics of the metalsemiconductor junction with high contact resistance have been a serious issue in modern electronic devices. A schottky barrier contact exhibits an asymmetrical current voltage iv characteristic when the polarity of a bias voltage applied to the metal semiconductor. Whether a given metalsemiconductor junction is an ohmic contact or a schottky barrier depends on the schottky barrier height. Under this situation, when the current can be conducted in both directions of the ms contact, the contact is defined as the ohmic contact.
Ohmic contact ms junction with large js v small linearize iv characteristics. Fmde 6 where fs and fm are fermidirac distribution functions in metal and semiconductor respectively, and pe is the tunneling probability given by pe exp 2. Whether a given metal semiconductor junction is an ohmic contact or a schottky barrier depends on the schottky barrier height. This implies that the free carrier density at and in the vicinity of the contact is much greater than that in the bulk of the semiconductor e. Semiconductor physics, quantum electronics and optoelectronics. Peartonc asandia national laboratories, albuquerque, nm 87185, usa blucent technologies, murray hill, nj 07974, usa cuniversity of florida, gainsville, fl 32611, usa abstract a survey of ohmic contact materials and properties to gaas, inp, gan will be.
Graphene for true ohmic contact at metalsemiconductor. B is significantly higher than the thermal energy kt, the semiconductor is depleted near the metal and behaves as a schottky barrier. Schottky barrier detectors are photodiodes with one schottky and one ohmic metalsemiconductor junction. Metal semiconductor contact anchit biswas techno india,saltlake 2. Ms will be ohmic ohmic contact occur when the induced charge in the semiconductor during the fermi level alignment is the majority carriers. Metalsemiconductor interfaces rectifying schottky junction nonrectifying ohmic contacts 4. Contact resistance to a thin semiconductor layer print file in pdf format. The heterostructure barrier layer can form a two dimensional free carrier gas for the contact at a heterointerface of the heterostructure barrier layer and the semiconductor layer.
For the junction to admit electrons easily in both directions ohmic contact, the barrier height must be small in at least some parts of the junction surface. Schottky diode is a metalsemiconductor junction diode that has less forward voltage drop than the pn junction diode and can be used in highspeed switching applications. It is well known that the quality of metalsemiconductor contacts plays an important role in the performance of various semiconductor devices and integrated circuits. Pdf the study of ohmic contacts to wide bandgap semiconductors proves that when metalsemiconductor contacts are deposited, they commonly result in. Introduction formation of barrier current transport processes measurement of barrier height device structures ohmic contact metal. In such case, the carriers are free to flow in or out of the semiconductor so that there is a minimal resistance across the contact. Including barrier height calculator and depletion width calculator. A metalsemiconductor junction results in an ohmic contact i.
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