Paste for ohmic contact to P-type semiconductor and method for forming ohmic contact to P-type semiconductor using the same

Abstract

The present disclosure relates to a paste for ohmic contact to p-type semiconductor, including a metal oxide and a binder, wherein the metal oxide is a rhenium oxide or a molybdenum oxide.

Claims

1. A method for forming an ohmic contact to a p-type semiconductor, comprising: applying a paste to a flexible GaN substrate, drying the paste on the flexible GaN substrate without a vacuum process or a thermal process, and performing a surface treatment of the flexible GaN substrate, wherein the paste comprises a metal oxide and a binder, wherein the metal oxide is a rhenium oxide or a molybdenum oxide, and wherein the binder is an inorganic or organic polymer compound.

2. The method of forming the ohmic contact to p-type semiconductor according to claim 1, wherein the metal oxide is rhenium oxide and wherein the rhenium oxide includes at least one selected from Re.sub.2O, Re.sub.2O.sub.3, ReO.sub.2, ReO.sub.3 and Re.sub.2O.sub.7.

3. The method of forming the ohmic contact to p-type semiconductor according to claim 1, wherein the metal oxide is molybdenum oxide and wherein the molybdenum oxide includes at least one selected from Mo.sub.2O, Mo.sub.2O.sub.3, MoO.sub.2, MoO.sub.3 and Mo.sub.2O.sub.7.

4. The method of forming the ohmic contact to p-type semiconductor according to claim 1, wherein the organic polymer compound is present and the organic polymer compound includes at least one selected from a vinyl-based polymer compound, a polyamide-based polymer compound and a polyurethane-based polymer compound.

5. The method of forming the ohmic contact to p-type semiconductor according to claim 4, wherein the vinyl-based polymer compound is present and the vinyl-based polymer compound is polyvinylalcohol.

6. The method of forming the ohmic contact to p-type semiconductor according to claim 5, wherein the polyvinylalcohol is present in an amount ranging between 0.03 and 0.15 mL.

7. The method of forming the ohmic contact to p-type semiconductor according to claim 1, wherein the rhenium oxide is present and includes ReO.sub.2, and the binder includes 0.15 mL of polyvinylalcohol.

8. The method of forming the ohmic contact to p-type semiconductor according to claim 1, wherein the molybdenum oxide is present and includes MoO.sub.2, and the binder includes 0.10 mL of polyvinylalcohol.

9. The method for forming ohmic contact to p-type semiconductor according to claim 1, wherein the performing surface treatment of the flexible GaN substrate comprises immersing in a solvent and boiling aqua regia.

10. The method for forming ohmic contact to p-type semiconductor according claim 5, wherein the polyvinylalcohol is present in an amount ranging between 0.05 milligrams to 0.25 milligrams, per milligram of the metal oxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram of a substrate and a paste for ohmic contact to p-type semiconductor according to an embodiment of the present disclosure.

(2) FIG. 2 is a diagram showing each step of a method for forming ohmic contact to p-type semiconductor according to an embodiment of the present disclosure.

(3) FIG. 3 shows electrical resistance characteristics of metal oxide MoO.sub.2 and ReO.sub.2 as a function of PVA content according to an embodiment of the present disclosure.

(4) FIG. 4A shows linear I-V characteristics of metal oxide contact on p-type Si according to an embodiment of the present disclosure.

(5) FIG. 4B shows specific contact resistance characteristics of metal oxide on p-type Si extracted by the TLM according to an embodiment of the present disclosure.

(6) FIG. 5A shows I-V characteristics of a p-type GaN substrate with metal oxide MoO.sub.2 ohmic contact as a function of PVA content according to an embodiment of the present disclosure.

(7) FIG. 5B shows I-V characteristics of a p-type GaN substrate with metal oxide ReO.sub.2 ohmic contact as a function of PVA content according to an embodiment of the present disclosure.

(8) FIG. 6 shows I-V characteristics of ReO.sub.2 contact on a p-type GaN substrate after surface treatment according to an embodiment of the present disclosure.

(9) FIG. 7 shows a method for forming ohmic contact to p-type semiconductor according to the related art.

DETAILED DESCRIPTION

(10) Hereinafter, a paste for ohmic contact to p-type semiconductor according to the present disclosure and a method for forming ohmic contact to p-type semiconductor using the same will be described through the preferred embodiments of the present disclosure on the basis of the accompanying drawings.

(11) Prior to the description, in many embodiments, elements with the same configuration will be representatively described in an embodiment using the same symbol, and in the other embodiments, only different elements will be described.

(12) FIG. 1 is a diagram of a substrate 100 and a paste 110 for ohmic contact to p-type semiconductor according to an embodiment of the present disclosure.

(13) As shown in FIG. 1, in the paste 110 material for forming ohmic contact, the present disclosure uses a metal oxide 111 and a binder 112. Specifically, for the metal oxide 111, rhenium (Re) or molybdenum (Mo) oxide is used.

(14) The rhenium oxide may be used as a material for forming ohmic contact to p-type semiconductor including at least one type of material selected from Re.sub.2O, Re.sub.2O.sub.3, ReO.sub.2, ReO.sub.3 and Re.sub.2O.sub.7.

(15) Additionally, the molybdenum oxide may be used as a material for forming ohmic contact to p-type semiconductor including at least one type of material selected from Mo.sub.2O, Mo.sub.2O.sub.3, MoO.sub.2, MoO.sub.3 and Mo.sub.2O.sub.7.

(16) Additionally, for the binder 112, an inorganic or organic polymer compound may be used, and the organic polymer compound may include at least one selected from a vinyl-based polymer compound, a polyamide-based polymer compound and a polyurethane-based polymer compound. Particularly, for the vinyl-based polymer compound, it is preferred to use polyvinylalcohol (PVA).

(17) The application of the paste 110 using the rhenium or molybdenum oxide and the binder to the substrate 100, followed by treatment of the substrate 100, may greatly improve the ohmic contact characteristics.

(18) FIG. 2 is a diagram showing each step of a method for forming ohmic contact to p-type semiconductor according to an embodiment of the present disclosure.

(19) As shown in FIG. 2, all substrates (glass, Si and GaN) are cleaned with a general solvent and prepared (S1), and the Si substrate is immersed in 10% dilute HF before deposition. Metal oxide powder 111 and 5 wt % of PVA are mixed on the substrates patterned with Kapton tape (S2), applied to the substrate 100 (S3), and dried in the air (S4).

(20) To improve the ohmic contact characteristics, surface treatment (S5) for oxide removal from the GaN substrate is each performed using a buffered oxide etch (BOE) and boiling aqua regia (HNO.sub.3:HCl=1:3) for 10 minutes and 20 minutes.

(21) Additionally, specific contact resistance characteristics on p-type Si are investigated using an optimized metal oxide mixture evaluated by electrical resistivity of the p-type semiconductor and contact state on the substrate. Additionally, to investigate Schottky barrier characteristics, metal oxide n-type silicon Schottky barrier diodes are fabricated.

(22) FIG. 3 shows electrical resistance characteristics of metal oxide MoO.sub.2 and ReO.sub.2 as a function of PVA content according to an embodiment of the present disclosure.

(23) As shown in FIG. 3, when the mixture of 5 wt % of PVA and metal oxide is applied to the glass substrate, electrical resistance is measured by Hall effect measurements as a function of PVA content in 30 mg of metal oxide powder.

(24) Specifically, it can be seen that ReO.sub.2 has lower resistance than MoO.sub.2, and the electrical resistance reduces with the increasing PVA content irrespective of metal oxide. Additionally, as the PVA content is lower, the bond strength of powder is lower and the resistance is higher, causing a contact problem of a probe tip.

(25) Meanwhile, an amount of binder in the mixture is very important because it may change the characteristics of metal oxide powder. Accordingly, a minimum amount of PVA for strongly binding the oxide powder is optimized. The optimized minimum amount of binder is evaluated by resistivity of the mixture and contact state on the substrate.

(26) Because the density of MoO.sub.2 and ReO.sub.2 (6.47 and 11.4 g/cm.sup.3 respectively) is different, the resistivity of the metal oxide mixture starts to reduce at different points, and at the point where the resistivity falls (in FIG. 1, where an amount of PVA in MoO.sub.2 is 0.1 mL and an amount of PVA in ReO.sub.2 is 0.05 mL), PVA in similar amounts is mixed in the same volume. The resistivity of the optimized mixture is 0.067.80.01 .Math.cm and 0.0230.004 .Math.cm in MoO.sub.2 and ReO.sub.2 respectively.

(27) FIG. 4A shows linear I-V characteristics of metal oxide contact on p-type Si according to an embodiment of the present disclosure.

(28) As shown in FIG. 4A, considering barrier formation in the energy band diagram, characterization of contacts of metal oxide is performed by forming contacts on p-type Si (=9.77 .Math.cm and N.sub.p=1.8710.sup.15 cm.sup.3, measured by the Hall effect).

(29) Additionally, the linear I-V characteristics show no barrier between the contacting parts of p-type Si and metal oxide. Furthermore, it is shown that the work function of p-type Si is 4.91 eV (.sub.Si=4.05 eV, bandgap=1.12 eV, E.sub.FiE.sub.F=0.304 eV), and the work function of metal oxide is 4.9 eV or higher.

(30) Accordingly, it can be seen that MoO.sub.2 and ReO.sub.2 all have much higher work function than p-type Si, and ohmic contacts are easily formed.

(31) FIG. 4B shows specific contact resistance characteristics of metal oxide on p-type Si extracted by the transmission line method (TLM), according to an embodiment of the present disclosure.

(32) As shown in FIG. 4B, the extracted specific contact resistance is 3.8180.15 and 2.4070.11 .Math.cm.sup.2 in MoO.sub.2 and ReO.sub.2 respectively. It can be seen that the extracted specific contact resistance is higher than the contact resistance 10.sup.3 .Math.cm.sup.2) of SiAl alloy on p-type Si formed by heat treatment at the melting temperature (577 C.), but it cannot be directly compared with metal alloy contact due to a difference in specific resistance of metal oxide and the use of non-vacuum and non-thermal process in the operation.

(33) FIGS. 5A and 5B each show I-V characteristics of a p-type GaN substrate with metal oxide MoO.sub.2 and ReO.sub.2 ohmic contact as a function of PVA content according to an embodiment of the present disclosure.

(34) Specifically, a 1 m-thick p-type GaN:Mg layer is grown on 2 m undoped GaN deposited on a sapphire substrate. In this instance, the carrier concentration of the p-type GaN film measured by the Hall effect measurements is 1.47*10.sup.16 cm.sup.3 (=31.14 .Math.cm). Additionally, because GaN has a wide energy bandgap (3.4 eV) and electron affinity (4.1 eV), the work function of p-type GaN is a value obtained by subtracting an energy difference between Fermi level E.sub.F and valance band maximum E.sub.V (N.sub.V=1.4510.sup.19 cm.sup.3) from the sum of the energy bandgap and the electron affinity.

(35) Accordingly, p-type GaN has the work function of 7.3 eV, and metal for forming ohmic contact should have theoretically high work function.

(36) Additionally, as shown in FIGS. 5A and 5B, it can be seen that the I-V curve is also influenced by the PVA content, and ReO.sub.2 has better contact characteristics than MoO.sub.2. This implies that ReO.sub.2 has not only higher electrical conductivity but also higher work function than MoO.sub.2.

(37) Additionally, it can be seen from the linear I-V characteristics showing that in the case of ReO.sub.2, the work function of ReO.sub.2 is not high enough to remove barrier to the p-type GaN, but it is close to the work function of GaN and forms a very low barrier height.

(38) FIG. 6 shows I-V characteristics of ReO.sub.2 contact on the p-type GaN substrate after surface treatment according to an embodiment of the present disclosure.

(39) Surface oxide acts as a barrier against carrier transport, affecting the contact characteristics. Accordingly, many researchers have studied various surface treatment methods to reduce the barrier. In the present disclosure, boiling aqua regia of HNO.sub.3:HCl=1:3 does not etch GaN, and effectively reduces the concentration of oxygen atoms on the surface.

(40) Additionally, surface treatment is each performed using BOE and boiling aqua regia for 10 minutes and 20 minutes. This treatment effectively removes surface oxide and reduces the barrier, thereby obtaining excellent linear I-V characteristics (ohmic contact) using boiling aqua regia without vacuum and thermal process.

(41) Particularly, oxide powder mixed with the binder used in the present disclosure is a metal oxide compound with high work function, and thus forms low metal semiconductor contact barriers when contacted with p-type semiconductor, facilitating the flow of carriers. Furthermore, without vacuum and thermal process, the process is made simpler and the cost savings are achieved.

(42) Additionally, 5 wt % of polyvinylalcohol (PVA) as a binder is added to molybdenum and rhenium oxide powder with high work function to prepare a paste without vacuum process and thermal process, thereby overcoming the limitation in obtaining ohmic contacts because of higher work function of the p-type semiconductor materials than available contact metals on Earth.

(43) Additionally, because ohmic characteristics are optimized with an addition of PVA in various amounts, it is possible to form ohmic contacts to p-type semiconductors using the MoO.sub.2 and ReO.sub.2 paste with high work function through non-vacuum and non-thermal process.

(44) Those skilled in the art will appreciate that the present disclosure may be embodied in other specific forms without changing the technical spirit or essential features.

(45) Therefore, it should be understood that the embodiments described hereinabove are for illustration only in all aspects, but not intended to limit the present disclosure to the above-described embodiments, and it should be interpreted that the scope of the present disclosure is defined by the appended claims rather than the above-described detailed description, and all modifications or variations derived from the meaning and scope of the appended claims and the equivalent concept are included in the scope of the present disclosure.