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. Pdf the study of ohmic contacts to wide bandgap semiconductors proves that when metalsemiconductor contacts are deposited, they commonly result in. Metalsemiconductor interfaces rectifying schottky junction nonrectifying ohmic contacts 4. Effect is different in inas as any metal becomes ohmic.
Metal semiconductor contact anchit biswas techno india,saltlake 2. It consists of a metal contacting a semiconductor surface, or junction. For example, good ohmic contacts are essential for achieving excellent electrical characteristics of a semiconductor device, while schottky i. How i tricked my brain to like doing hard things dopamine detox duration. Semiconductor physics, quantum electronics and optoelectronics. Pdf ohmic contacts for high power and high temperature. 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. Metalsemiconductor junction an overview sciencedirect. 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. Metalsemiconductor ohmic contacts stanford university.
An ohmic contact to a semiconductor layer including a heterostructure barrier layer and a metal layer adjacent to the heterostructure barrier layer is provided. The sign convention of the applied voltage and current is also shown in figure 1. A schottky barrier contact exhibits an asymmetrical current voltage iv characteristic when the polarity of a bias voltage applied to the metal semiconductor. In a normal pn junction diode, a ptype semiconductor and an ntype semiconductor are used to form the pn junction. Ee311 saraswat ohmic contacts 5 for a tunneling contact the net semiconductor to metal current is given by jsm at k. Semiconductor contacts physics of semiconductor devices wiley online library. Whether a given metalsemiconductor junction is an ohmic contact or a schottky barrier depends on the schottky barrier height. Schottky barrier diodes sufficiently that it is widely used. B is significantly higher than the thermal energy kt, the semiconductor is depleted near the metal and behaves as a schottky barrier. 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. Metalsemiconductor interfaces rectifying schottky junction nonrectifying ohmic contacts 3. 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.
Herein, we demonstrated the conversion of the schottky nature of the nisi junction, one of the most commonly used metalsemiconductor junctions, into an ohmic contact with low contact resistance by. 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. Ga 2 o 3 layer that can be mildly ndoped or even undoped. For a sufficiently large schottky barrier height, where. Sma5111 compound semiconductors lecture 2 metal semiconductor junctions outline introduction structure what are we talking about. It is well known that the quality of metalsemiconductor contacts plays an important role in the performance of various semiconductor devices and integrated circuits. Then the depletion region width at the metal semiconductor interface xd 2 k. Suppose nd or na in the semiconductor is very large. Metalsemiconductor contacts schottky and ohmic youtube.
Under this situation, when the current can be conducted in both directions of the ms contact, the contact is defined as the ohmic contact. 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. 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. A metalsemiconductor junction results in an ohmic contact i. 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. 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. Metalsemiconductor contacts fermi level pinning is the lack of barrier height modulation with metal work function due to either large density of intrinsic states.
The small barrier that exists for electron flow from metal to the semiconductor, but vanishes when. Metalsemiconductors contacts engineering libretexts. Schottky barrier detectors are photodiodes with one schottky and one ohmic metalsemiconductor junction. Whether a given metal semiconductor junction is an ohmic contact or a schottky barrier depends on the schottky barrier height. Importance of metalsemiconductor contacts is due to 1 ohmic metalsemiconductor junctions e. The term metalsilicon contact includes silicidesi contacts. Fermi level depinning and contact resistivity reduction. Conduction mechanisms for metalnsemiconductor contacts as a function of the barrier height and width. For lower schottky barrier heights, the semiconductor. Metal semiconductor interfaces rectifying schottky junction nonrectifying ohmic contacts 4. The term metal silicon contact includes silicidesi contacts. An ideal ohmic contact is a low resistance, and nonrectifying junction with no potential exists between the the metal semiconductor interface. When a metal and semiconductor are brought into contact, there are two types of junctions formed depending on the work function of the. 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.
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. 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. It is also claimed that electrons have tendency to flow when no potent. Schottky barrier determined by surface states rather than metal and semiconductor workfunction difference. The rectifying schottky characteristics of the metalsemiconductor junction with high contact resistance have been a serious issue in modern electronic devices. 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. An ideal ohmic contact is a low resistance, and nonrectifying junction with no potential exists between the the metalsemiconductor interface. Contact resistance to a thin semiconductor layer print file in pdf format.
A survey of ohmic contacts to iiiv compound semiconductors. Ms will be ohmic ohmic contact occur when the induced charge in the semiconductor during the fermi level alignment is the majority carriers. Metal semiconductor interfaces rectifying schottky junction nonrectifying ohmic contacts 3. 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. Introduction formation of barrier current transport processes measurement of barrier height device structures ohmic contact metal. Metalsemiconductor ohmic and schottky contacts byu. Graphene for true ohmic contact at metalsemiconductor. Sma5111 compound semiconductors lecture 2 metalsemiconductor junctions outline introduction structure what are we talking about. A survey of ohmic contacts to iiiv compound semiconductors a. Ohmic contact ms junction with large js v small linearize iv characteristics.