News Column

Patent Application Titled "Compound Semiconductor Device and Manufacturing Method Thereof" Published Online

February 27, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventors IMANISHI, Kenji (Kawasaki, JP); KIKKAWA, Toshihide (Kawasaki, JP), filed on October 10, 2013, was made available online on February 13, 2014.

The assignee for this patent application is Fujitsu Limited.

Reporters obtained the following quote from the background information supplied by the inventors: "In recent years, development of an electron device (compound semiconductor device) in which a GaN layer and an AlGaN layer are sequentially formed over a substrate, and the GaN layer is used as an electron transit layer is performed vigorously. A GaN based high electron mobility transistor (HEMT) is cited as one of the compound semiconductor devices as stated above. In the GaN based HEMT, high-concentration two-dimensional electron gas (2DEG) generated at a heterojunction interface between AlGaN and GaN is used.

"A band gap of GaN is 3.4 eV, which is larger than a band gap of Si (1.1 eV) and a band gap of GaAs (1.4 eV). Namely, GaN has high breakdown electric field intensity. Besides, GaN also has large saturation electron velocity. Accordingly, GaN is very expectable as a material of a compound semiconductor device capable of high-voltage operation and high-power. The GaN based HEMT is expected as a high breakdown-voltage electronic device used for a high-efficiency switching element, an electric vehicle, and so on.

"The GaN based HEMT using the high-concentration two-dimensional electron gas performs a normally-on operation in many cases. Namely, a current flows when a gate voltage is turned off. This is because a number of electrons exist at a channel. On the other hand, a normally-off operation is regarded as important from a point of view of fail-safe for the GaN based HEMT used for the high breakdown-voltage electronic device.

"Accordingly, various investigations have been done as for the GaN based HEMT capable of the normally-off operation. For example, a structure in which a p-type semiconductor layer is provided between a gate electrode and an active region is proposed. Besides, a structure dividing the 2DEG by etching an electron supply layer just below the gate electrode is also proposed.

"However, doping of p-type impurities and a heat treatment for activation are necessary to obtain the structure providing the p-type semiconductor layer. It is necessary to increase a temperature of the heat treatment to high temperature because the p-type impurities are extremely difficult to be activated compared to n-type impurities, and mobility of electrons is lowered because an interface between the electron transit layer and the electron supply layer is damaged during the high-temperature heat treatment. Besides, significant damage occurs in a vicinity of the electron transit layer in the etching to obtain the structure in which the 2DEG is divided, and therefore, there are cases when a sheet resistance increases and leak current increases. Accordingly, it is difficult to apply these technologies to actual devices.

"Patent Literature 1: Japanese Laid-open Patent Publication No. 2007-19309

"Patent Literature 2: Japanese Laid-open Patent Publication No. 2009-76845"

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "According to an aspect of a compound semiconductor device, a substrate; a first AlGaN layer formed over the substrate; a second AlGaN layer formed over the first AlGaN layer; an electron transit layer formed over the second AlGaN layer; and an electron supply layer formed over the electron transit layer are provided. A relationship of '0.ltoreq.x1

"According to an aspect of a manufacturing method of a compound semiconductor device, a first AlGaN layer is formed over a substrate. A second AlGaN layer is formed over the first AlGaN layer. An electron transit layer is formed over the second AlGaN layer. An electron supply layer is formed over the electron transit layer. A relationship of '0.ltoreq.x1

"The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

"It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

"FIG. 1A and FIG. 1B are views illustrating a structure of a GaN based HEMT according to an embodiment;

"FIG. 2A to FIG. 2H are sectional views illustrating a manufacturing method of the GaN based HEMT according to the embodiment in process sequence;

"FIG. 3 is a view representing a depth-profile of electron energy and electron density of the GaN based HEMT according to the embodiment;

"FIG. 4 is a sectional view illustrating a structure of a reference;

"FIG. 5 is a view representing a depth-profile of electron energy and electron density of a GaN based HEMT according to the reference;

"FIG. 6 is a view representing a relationship between a gate voltage and a density of two-dimensional electron gas;

"FIG. 7 is a view illustrating an example of an external appearance of a high power amplifier; and

"FIG. 8A and FIG. 8B are views illustrating a power supply device."

For more information, see this patent application: IMANISHI, Kenji; KIKKAWA, Toshihide. Compound Semiconductor Device and Manufacturing Method Thereof. Filed October 10, 2013 and posted February 13, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=2714&p=55&f=G&l=50&d=PG01&S1=20140206.PD.&OS=PD/20140206&RS=PD/20140206

Keywords for this news article include: Treatment, Electronics, Semiconductor, Fujitsu Limited.

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Source: Politics & Government Week


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