National Science Council

National Cheng-kung University

National Science Council of Republic of China

National Science Counsel of Republic of China

Wen-Chau Liu

Shiou-Ying Cheng

Jung-Hui Tsai

Lih-Wen Laih

Huey-Ing Chen

Wen-Shiung Lour

Kun-Wei Lin

Hsi-Jen Pan

Chung-Fu Chang

Tsung-Han Tsai

Chin-Yi Chu

Tai-You Chen

Yen-I Chou

Wen-Lung Chang

Chi-Hsiang Hsu

Kuo-Hui Yu

Wei-Chou Wang

Chun-Tsen Lu

Huey-lng Chen

The present invention is a multi-gas sensor and a method for fabricating the multi-gas sensor. The multi-gas sensor comprises a substrate, an epitaxial layer, a metal oxide layer, a first metal layer, a second metal layer and multiple third metal layers. The method for fabricating the multi-gas sensor comprises steps of forming an epitaxial layer on a substrate; etching the epitaxial layer to form a first epitaxial structure and a second epitaxial structure a fixed distance from the first epitaxial structure; forming a metal oxide layer on the first epitaxial structure; forming a first metal layer that has at least two metal layers on the second epitaxial structure; forming a second metal layer a fixed distance from the first metal layer on the second epitaxial structure; forming third metal layers respectively on the metal oxide layer, the first metal layer and the second metal layer.

Multi-gas sensor and method of fabricating the sensor

A semiconductor diode with hydrogen detection capability includes a semiconductor substrate, a doped semiconductor active layer formed on the substrate and made from a compound having the formula XYZ, in which X is a Group III element, Y is another Group III element different from X, and Z is a Group V element, a semiconductor contact-enhancing layer formed on the active layer and made from a compound having the formula MN, in which M is a Group III element, and N is a Group V element, an ohmic contact layer formed on the semiconductor contact-enhancing layer, and a Schottky barrier contact layer formed on the active layer. The Schottky barrier contact layer is made from a metal that is capable of dissociating a hydrogen molecule into hydrogen atoms.

Semiconductor diode capable of detecting hydrogen at high temperatures

A high-sensitivity Pd/InP hydrogen sensor was made by a) forming an n-type or p-type semiconductor film on a semiconductor substrate; b) forming a patterned first metal electrode on the semiconductor film, wherein the first metal electrode forms an Ohmic contact with the semiconductor film; and c) forming a second metal electrode on the semiconductor film, the second metal electrode being isolated from the first metal electrode, wherein the second metal electrode forms a Schottky contact with the semiconductor film, wherein a thickness of the second metal electrode and a material of which the second metal electrode is made enable a Schottky barrier height of the Schottky contact to decrease when hydrogen contacts the second metal electrode. The second metal electrode can be physical vapor deposited or electroless plated.

Process for preparing a hydrogen sensor

A bipolar heterojunction transistor (HBT) includes a collector layer, a base layer formed on the collector layer, a first transition layer formed on the base layer, an emitter layer formed on the first transition layer, a second transition layer formed on the emitter layer, and an emitter cap layer formed on the second transition layer. Each of the first and second transition layers is formed of a composition that contains an element, the mole fraction of which is graded in such a manner that the conduction band of the HBT is continuous through the base layer, the first and second transition layers, the emitter layer and the emitter cap layer.

Heterojunction bipolar transistor with zero conduction band discontinuity

The invention relates to a high-breakdown voltage heterostructure field-effect transistor (FET), which can be used under a high temperature condition. The FET device from bottom upward in succession includes a semiconductor substrate, a buffer layer, a delta-doped sheet, an undoped layer, a sub-channel layer, an active channel layer, a gate layer, and an ohmic contact layer.

High-breakdown voltage heterostructure field-effect transistor for high temperature operations

An InP/InGaAlAs heterojunction bipolar transistor with the characteristics of amplification and negative-differential-resistance phenomenon is presented in the invention. The 3-terminal current-voltage characteristics of the heterojunction bipolar transistor can be controlled by the applied base current. In the large collector current regime, the heterojunction bipolar transistor has the characteristics as similar to conventional bipolar junction transistors. However, in a small collector current regime, both the transistor active region and negative-differential-resistance loci are observed. The negative-differential-resistance phenomenon is caused by the insertion of a thin base layer and a &dgr;-doped sheet. Moreover, the use of a setback layer with a thickness of 50 &angst; added at the emitter-base junction can suppress the diffusion of doping impurity in the base and reduce the potential spike at emitter-base heterojunction so as to improve the confinement of holes injected from base to emitter.

Negative-differential-resistance heterojunction bipolar transistor with topee-shaped current-voltage characteristics

In this invention, we propose a high-sensitivity Pd/InP hydrogen sensor. First, a n-type InP semiconductor membrane is grown on a semi-insulating InP substrate. The concentration and thickness of this membrane are 2&times;10,cm,and 3000 &angst;, respectively. Then, Pd metal and AuGe alloy are evaporated on the surface of the membrane as the anode and cathode electrodes, respectively. Due to the catalytic performance of Pd metal, the adsorbed hydrogen molecules on the surface of the Pd metal are dissociated into hydrogen atoms. The hydrogen atoms diffuse and pass through the Pd metal and form a dipole layer at the interface between the Pd metal and the n-type InP membrane. This dipole layer will decrease the depletion width of the n-type InP membrane and further lower the metal-semiconductor Schottky barrier height. Therefore, the current-voltage (I-V) characteristics will be modulated after the introduction of hydrogen gas.

Hydrogen sensor

The present invention provides a structure of a metal-insulator-semiconductor (MIS)-like multiple-negative-differential-resistance (MNDR) device and the fabrication method thereof. The device of the present invention has the characteristics of dual-route and MNDR at low temperatures. These characteristics result from the successive barrier-lowering and potential-redistribution effect when conducting carriers fall into a quantum well. MNDR devices have excellent potential in multiple-value logic circuitry applications and are capable of reducing circuitry complexity.

Structure of metal-insulator-semiconductor-like multiple-negative-differential-resistance device and fabrication method thereof

In this invention, a new, simple and small-size hydrogen-sensitive palladium (Pd) membrane/semiconductor Schottky diode sensor has been developed and fabricated. First, a high quality undoped GaAs buffer layer and an n-type GaAs epitaxial layer with the carrier concentration of 2.times.10.sup.17 cm.sup.31 3 is grown by molecular beam epitaxy (MBE) on a semi-insulated GaAs substrate. Then a thin Pd membrane is evaporated on the surface of the n-type GaAs epitaxial layer by the vacuum evaporation technique. It is well-known that palladium metal has excellent selectivity and sensitivity on hydrogen gas. When hydrogen gas diffuses to the Pd membrane surface, the hydrogen molecules will dissociate into hydrogen atoms. Some of the hydrogen atoms diffuse through the thin metal layer and form the palladium hydride near the metal-semiconductor interface. The hydride may effectively lower the work function of Pd metal. The lowering of work function results in the reduction of Schottky barrier height at the Pd metal-GaAs semiconductor interface and the modification in the measured current-voltage characteristics of the studied device. Experimental results reveal that, during the hydride formation process, the forward- and reverse-biased currents are increased by the increase of hydrogen concentration. It also demonstrates that the Schottky barrier height is indeed decreased with increasing the hydrogen concentration. Therefore, the studied device can be used in fabricating a high-performance hydrogen-sensitive sensor.

Hydrogen-sensitive palladium (PD) membrane/semiconductor schottky diode

The invention is to develop a high-speed low power consumption resonant tunneling element--a superlatticed negative-differential-resistance (NDR) functional transistor. The proposed element exhibits amplification and obvious NDR phenomena simultaneously. In this element, the emitter region includes 5-period GaInAs/AlInAs super lattice resonant tunneling and emitter layers. Since the emitter--base interface is of homojunction, the collector--emitter offset voltage (V.sub.CE, offset) may be lowered down significantly. In addition, the produced infinitesimal potential (.DELTA.Ev) at GaInAs/AlInAs interface due to heterojunction in discrete valence bands may be applied as barriers to prohibit holes flow from base towards emitter. By doing so, the base current is remarkably depressed so as to elevate efficiency of emitter injection as well as current gain.

Superlatticed negative-differential-resistance functional transistor

The present provides two low offset voltage AlInAs/GaInAs heterostructure-confinement bipolar transistors which include AlInAs heterostructure-confinement and AlInAs/GaInAs superlattice-confinement bipolar transistors. In the present invention, an n GaInAs emitter layer is inserted at AlGaAs confinement layer/GaInAs base layer to reduce offset voltage and potential spike at an E-B junction.

Low offset voltage AlInAs/GaInAs heterostructure-confinement bipolar

The present invention provides a GaInP/GaInAs/GaAs modulation-compositioned channel field-effect transistor which comprises: a substrate of semi-insulated GaAs material; a first layer of non-doped GaAs material, formed on the substrate; a second layer of n-doped GaInAs material, formed on the first layer; a third layer of non-doped GaInP material, formed on the second layer; a fourth layer of n-doped GaAs material, formed on the third layer; an Au layer, formed on the third layer; and an Au/Ge/Ni alloy layer, formed on the fourth layer. An accumulation effect is performed because there is a V-shaped energy band existing in the modulation-compositioned channel. Therefore, the transistor of the present invention is characterized by a large current density, a large gate voltage swing with high transconductance, and a high gate breakdown voltage. The present invention has a good potentiality for high-speed, high-power, and large input signal circuit applications.

GaInP/GaInAs/GaAs modulation-compositioned channel field-effect

Structure of metal-insulator-semiconductor-like

A new high-speed resonant tunneling device, namely, a long-period superlattice resonant tunneling transistor, is developed according to the invention. The structure of the proposed 20-period superlattice resonant tunneling transistor consists of an InP substrate, a buffer layer formed by GaInAs material on the substrate, a collector layer formed by GaInAs material on the buffer layer, a base layer formed by GaInAs material on the collector layer, an emitter layer formed by GaInAs material on the base, a 20-period superlattice resonant tunneling layer formed by AlInAs and GaInAs materials on the emitter layer, and an ohmic contact layer formed by GaInAs material on the 20-period superlattice resonant tunneling layer. Furthermore, the emitter region includes a 20-period AlInAs/GaInAs superlattice and an emitter layer. Due to the presence of an emitter-base homojunction, collector-emitter offset voltage (V.sub.CE,offset) can be reduced significantly. In addition, the valence band discontinuity (.DELTA.Ev) at the AlInAs/InGaAs heterojunction may be used as a barrier for holes injected from the base toward the emitter region. Therefore, the emitter injection efficiency and current gain can be increased. From the theoretical analysis and computer simulation, two subbands are observed in the superlattice region. Under the proper applied bias, the studied device will create n-type negative differential resistance (NDR). Consequently, the proposed device shows good promise for use in amplification, parity generator, and multiple-value logic circuit applications.

Long-period superlattice resonant tunneling transistor

The invention relates to the structure of the camel-gate field-effect transistor with multiple modulation-doped channels. The device structure, from the bottom to the top in succession, includes the substrate, the buffer layer, the multiple modulation-doped channels, the thin and complete depletion layer, and the ohmic contact layer. The transistor is characterized by a camel-gate diode, which is composed of the multiple modulation-doped channels, the thin and complete depletion layer and the ohmic contact layer. The gate structure may achieve the high potential height between the gate electrode and the source electrode as well as the high breakdown voltage performance. Furthermore, the use of multiple modulation-doped channels, made of n-type GaAs materials with different thickness and doped concentration, can exhibit excellent properties of high output current, large and linear transconductances.

Growing community of inventors

Tainan, Taiwan

Wen-Chau Liu