Epitaxial substrate for electronic device and method of producing the same

#The present invention relates to an epitaxial substrate for an electronic device and a method of producing the same, in particular, to an epitaxial substrate for HEMT and a method of producing the same.

#In recent years, HEMT (High electron mobility transistor) has been widely used as high-speed FET (Field effect transistor) as speed required of an IC device increases. Such a FET-type transistor as described above is generally formed, as schematically illustrated in FIG. 1, for example, by laminating a channel layer 22 and an electron supply layer 23 on a substrate 21 and then providing a surface of the electron supply layer 23 with a source electrode 24, a drain electrode 25 and a gate electrode 26. When this transistor device is operated, electrons are moved through the source electrode 24, the electron supply layer 23, the channel layer 22, the electron supply layer 23 and the drain electrode 25 in this order, thereby defining the lateral direction of the device as a current conducting direction. This movement of electrons in the lateral direction is controlled by voltage applied on the gate electrode 26. In a HEMT, electrons generated at a joint interface between the electron supply layer 23 and the channel layer 22 of which band gaps are different from each other can move significantly fast, as compared with electrons in a conventional semiconductor.

#Movement of electrons in a lateral direction, i.e. electric current, is controlled by a gate voltage, as described above. Electric current generally does not drop to zero when a gate voltage is turned off and electric current flowing when a gate voltage is turned off is called “leakage current”. Increase in leakage current results in increase in power consumption, possibly causing problems such as heat generation. Leakage current is generally classified to lateral leakage current and vertical leakage current. Lateral leakage current represents leakage current flowing between two electrodes (e.g. the source electrode 24 and the drain electrode 25) provided on a surface of the electron supply layer 23. Vertical leakage current represents leakage current flowing between two electrodes disposed at a surface of the electron supply layer 23 and a surface of the substrate 21, respectively.

#FIG. 1 is a schematic sectional view showing a conventional field effect transistor.

#FIG. 2 is an schematic sectional view of an epitaxial substrate for an electronic device according to the present invention.

#FIGS. 3(a), 3(b) and 3(c) are graphs showing measurement results of withstand voltage in a lateral direction, lateral leakage current, and withstand voltage in the vertical direction, respectively.

#Next, an embodiment of an epitaxial substrate for an electronic device of the present invention will be described with reference to drawings. FIG. 2 schematically shows a sectional structure of an epitaxial substrate for an electronic device according to the present invention. The epitaxial substrate is illustrated with exaggeration in thickness direction thereof in FIG. 2 for conveniences in explanation.

#As shown in FIG. 2, the epitaxial substrate 1 for an electronic device of the present invention has a Si single crystal substrate 2, a buffer 3 as an insulating layer formed on the Si single crystal substrate 2, and a main laminated body 4 formed by plural group III nitride layers epitaxially grown on the buffer 3, wherein a lateral direction of the epitaxial substrate is defined as an electric current conducting direction. Specifically, the buffer 3 includes at least an initially grown layer 5 in contact with the Si single crystal substrate 2 and a superlattice laminate 6 constituted of a superlattice multilayer structure on the initially grown layer 5. The initially grown layer 5 is made of an AlN material. The superlattice laminate 6 is formed by alternate lamination of a first layer 6a made of a Ba1Alb1Gac1Ind1N (0≦a1≦1, 0≦b1≦1, 0≦c1≦1, 0≦d1<1, a1+b1+c1+d1=1) material and a second layer 6b made of a Ba2Alb2Gac2Ind2N (0≦a2≦1, 0≦b2≦1, 0≦c21, 0d2≦1, a2+b2+c2+d2=1) material having a band gap different from that of the first layer. Both of the superlattice laminate 6 and a portion 4′, on the buffer 3 side, of the main laminated body 4 has carbon (C) concentration of 1×1018/cm3 or higher. Due to the structure described above, it is possible not only to make decrease in lateral leakage current and achievement of good properties of withstand voltage in a lateral direction compatible but also enhance withstand voltage in the vertical direction.

#Crystal-face orientation of the Si single crystal substrate 2 is not particularly specified and (111) face, (100) face, (110) face or the like can be use. Use of (111) face is preferable in terms of growing (0001) face of group III nitrides with satisfactory surface flatness. The conduction type of the Si single crystal substrate 2 may be either p-type or n-type. Regarding conductivity of the Si single crystal substrate 2, any appropriate substrate ranging from a highly insulative substrate having high specific resistance of 10,000 Ω·cm or higher to a substrate having low specific resistance of 0.001 Ω·cm or so can be used depending on applications. Examples of possible production method of the Si single crystal substrate 2 include the CZ method, the FZ method and other methods of various types. Si, SiC and the like may be epitaxially grown on a surface of the substrate. It is also possible to use a substrate having a thin oxide, nitride or carbide film formed on a surface thereof.