Semiconductor diode capable of detecting hydrogen at high temperatures

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.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor diode, more particularly to a semiconductor diode that is capable of detecting hydrogen at high temperatures.

2. Description of the Related Art

In co-pending U.S. patent application Ser. No. 10/725,801, the applicant disclosed a semiconductor diode with hydrogen detection capability. The semiconductor diode 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 m element, Y is another Group III element different from X, and Z is a Group V element; an ohmic contact layer formed on the active layer; and a Schottky barrier contact layer formed on the active layer so as to provide a Schottky barrier therebetween. The Schottky barrier contact layer is made from a metal that is capable of dissociating a hydrogen molecule into hydrogen atoms. The active layer is preferably made from n-type InGaP or AlxGa1-xAs so as to impart the semiconductor diode with a capability of detecting hydrogen at high temperatures.

However, due to a relatively large difference in surface property between the ohmic contact and the active layer, the contact therebetween is relatively poor, which results in an increase in the electrical resistance of the semiconductor diode.

The whole disclosure of the co-pending U.S. patent application Ser. No. 10/725,801 is incorporated herein by reference.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a semiconductor diode for hydrogen detection that is capable of overcoming the aforesaid drawback associated with the co-pending U.S. patent application Ser. No. 10/725,801.

According to the present invention, there is provided a semiconductor diode with hydrogen detection capability that 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 m 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 extending through the semiconductor contact-enhancing layer and into the active layer; and a Schottky barrier contact layer formed on the active layer so as to provide a Schottky barrier therebetween. The Schottky barrier contact layer is made from a metal that is capable of dissociating a hydrogen molecule into hydrogen atoms.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1illustrates the preferred embodiment of a semiconductor diode10suitable for use in a hydrogen sensor according to the present invention. The semiconductor diode10includes: a semiconductor substrate12; a doped semiconductor active layer14formed on the substrate12and made from a compound having the formula XYZ, in which X is a Group III element, Y is another Group m element different from X, and Z is a Group V element; a semiconductor contact-enhancing layer15formed on the active layer14and 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 layer17formed on the semiconductor contact-enhancing layer15and extending through the semiconductor contact-enhancing layer15and into the active layer14; and a Schottky barrier contact layer16formed on the active layer14so as to provide a Schottky barrier therebetween. The Schottky barrier contact layer16is made from a metal that is capable of dissociating a hydrogen molecule into hydrogen atoms. The ohmic contact layer17is formed using vapor deposition techniques, and is subsequently annealed under a temperature of about 400° C. for about one about minute so as to permit extension thereof into the active layer14.

Preferably, the semiconductor contact-enhancing layer15is made from n-GaAs, has a dopant concentration ranging from 1×1017to 1×1019atoms/cm3, and has a thickness ranging from 100 to 3000 Å.

Preferably, an oxide layer18is sandwiched between the Schottky barrier contact layer16and the active layer14. The hydrogen atoms thus formed diffuse through the Schottky barrier contact layer16, and are trapped in the junction between the Schottky barrier contact layer16and the oxide layer18, which results in the formation of a dipole moment layer (seeFIG. 2) therebetween, which, in turn, results in an unbalance in the charge distribution therebetween. The aforesaid charge distribution reaches a new equilibrium state when the hydrogen atoms cease to diffuse through the Schottky barrier contact layer16. The dipole moment layer reduces the width of the depletion region of the active layer14and the Schottky barrier of the Schottky barrier contact layer16.

The oxide layer18serves to broaden the variation range of the Schottky barrier, which results in an increase in the sensitivity of the semiconductor diode10. The oxide layer18is preferably made from a compound selected from the group consisting of silicone dioxide, titanium didoxide, and zinc oxide, and preferably has a thickness ranging from 20 to 500 Å.

Preferably, the compound of the active layer14is selected from the group consisting of n-type In0.49Ga0.51P and AlxGa1-xAs with x=0−1. The active layer14preferably has a dopant concentration ranging from 1×1015to 5×1018atoms/cm3, and a thickness ranging from 1000 to 5000 Å.

The substrate12is preferably made from semi-insulating GaAs. Preferably, a semiconductor buffer layer13is sandwiched between the substrate12and the active layer14, is made from undoped i-GaAs, and has a thickness ranging from 1000 to 50000 Å.

Preferably, the ohmic contact layer17is made from AuGe/Ni or Au/Ge, and has a thickness ranging from 1000 to 50000 Å.

Preferably, the metal of the Schottky barrier contact layer16is selected from the group consisting of Pt, Pd, Ni, Rh, Ru, and Ir. The Schottky barrier contact layer16preferably has a thickness ranging from 100 to 20000 Å.

The present invention will now be described in greater detail in connection with the following test results.

FIGS. 3 to 7show the test results of the preferred embodiment of the semiconductor diode10according to this invention.

FIG. 3shows the Schottky barrier heights of the preferred embodiment for different hydrogen concentrations. The results indicate that the higher the hydrogen concentration, the lower will be the resultant Schottky barrier heights and that the Schottky barrier heights decreases sharply in an exponential order at a low hydrogen concentration region.

FIG. 4shows I-V curves (forward biased) obtained during hydrogen detection under different hydrogen concentrations (i.e., air, i.e., zero ppm, 15 ppm, 48 ppm, 97 ppm, 202 ppm, 1010 ppm, and 9090 ppm) and different biased voltages. The results indicate that the higher the hydrogen concentration, the higher will be the resultant electric current.

FIG. 5shows measured sensitivity of the semiconductor diode10in detecting the presence of hydrogen under different detecting temperatures (i.e., 300K, 320K, 340K, 365K, 390K, 430K, and 470K) and under different hydrogen concentrations. The sensitivity (S) is defined as S(%)=(Ih−Ia)/Ia(%), in which Ihis the measured current in the presence of hydrogen in the air, and Iais the measured current without the presence of hydrogen in the air. The sensitivity test was conducted at a forward biased voltage of 0.35V. The results indicate that the higher the temperature, the lower will be the sensitivity for all the hydrogen concentrations, and that the higher the hydrogen concentration, the higher will be the sensitivity for all the detecting temperatures. Note that the increase in the sensitivity inFIG. 5is particularly evident under temperatures above 365K.

FIG. 6shows I-V curves (forward and reverse biased voltages) of the preferred embodiment during detection of hydrogen at a temperature of 95° C. under different hydrogen concentrations (i.e., zero ppm, 15 ppm, 97 ppm, 1010 ppm, and 9090 ppm). The results indicate that the semiconductor diode10of this invention is capable of detecting hydrogen under a high temperature environment.

FIG. 7shows the response time of the preferred embodiment during detection of hydrogen under different hydrogen concentrations. The response time of the semiconductor diode10was measured under a forward biased voltage of 0.35V at a temperature of 95° C. in a test chamber (not shown). The test chamber is connected to a hydrogen gas supply which supplies hydrogen into the test chamber in a rate of about 500 ml/min. The results show that the current rises steeply immediately after the hydrogen gas supply is turned on (indicated as reference mark “a” inFIG. 7) and drops sharply immediately after the hydrogen gas supply is turned off (indicated as reference mark “b” inFIG. 7). The hydrogen atoms trapped in the semiconductor diode10diffuse backward into the test chamber after the hydrogen gas supply is turned off, thereby resulting in recovery of electric current. The results indicate that the hydrogen-detecting semiconductor diode10has a response time of 302 seconds for 15 ppm hydrogen concentration, 40.3 seconds for 202 ppm hydrogen concentration, 13.2 seconds for 1010 ppm hydrogen concentration, and 4.5 seconds for 9090 ppm hydrogen concentration.

Compared to the semiconductor diode of the co-pending U.S. patent application Ser. No. 10/725,801, the semiconductor diode10of this invention exhibits a better surface contact between the ohmic contact17and the active layer14. Moreover, the material used for the semiconductor contact-enhancing layer15imparts the semiconductor diode10with a better compatibility to connect or integrate with other electronic devices.

With the invention thus explained, it is apparent that various modifications and variations can be made without departing from the spirit of the present invention.