Method and device for judging polarity of single crystal sample

#This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP2006/317095 filed Aug. 30, 2008.

#The present invention relates to a method and apparatus for judging the polarity of a single crystal sample with the use of an X-ray diffraction method.

#A III-V compound semiconductor crystal such as GaAs has a polarity (i.e., a direction of crystal) in its crystal structure. FIG. 5 is a perspective view showing the major crystal lattice planes of a GaAs crystal. The GaAs crystal structure belongs to the cubic system. Assuming that the top plane in FIG. 5 is a (100) plane, eight crystal lattice planes that are equivalent of a (111) plane in the simple cubic lattice (these crystal lattice planes are marked by cross hatching in FIG. 5 and they will be expressed by Ga{111} planes) are classified to a Ga plane on which only Ga atoms exist and an As plane on which only As atoms exist. In a direction perpendicular to such a crystal lattice plane, there appear alternately the Ga planes and the As planes with different distances having a three-to-one ratio. A viewing direction from the Ga plane to the nearest As plane is opposite to a viewing direction from the As plane to the nearest Ga plane, and it is considered that physical and chemical properties depend on such a direction. Such a difference in direction of crystal is referred to as a polarity. Among the eight crystal lattice planes belonging to Ga{111 }, the four equivalent crystal lattice planes (111), (1-1-1), (−11-1) and (−1-11) belonging to the Ga plane, these four crystal lattice planes being defined as a “positive polar plane”. On the other hand, the four equivalent crystal lattice planes (−1-1-1), (11-1), (1-11) and (−111) belong to the As plane, these four crystal lattice planes being defined as a “negative polar plane”. It is noted that the numbers in parentheses are the Miller indices and the minus sign should be attached to the trailing number after the minus sign. When the positive polar plane exists on the crystal surface, Ga atoms appear on the crystal surface. On the contrary, when the negative polar plane exists on the crystal surface, arsenic (As) atoms appear on the crystal surface.

#FIG. 1 It is a plan view showing an example of a configuration on of an X-ray diffraction apparatus, which is used for carrying out the polarity judging method according to the present invention.

#FIG. 2 It is a perspective view of a state in measuring a GaAs(333) plane with the apparatus shown in FIG. 1.

#FIG. 3 It is a perspective view of a state in measuring a GaAs(33-3) plane with the apparatus shown in FIG. 1.

#10 rotating target 11 X-ray focal spot 12 X-ray beam 14 multilayer mirror 16 parallel beam 18 sample 20 diffracted X-ray beam 22 X-ray detector 24 φ-axis 26 ω-axis 28 χ-axis 38 incident slit 39 four-crystal monochromator 40 goniometer base 42 2θ turntable 44 sample table 48 receiving slit

#Embodiments of the present invention will now be described in detail below with reference to the drawings. FIG. 1 is a plan view showing an example of a configuration on of an X-ray diffraction apparatus, which is used for carrying out the polarity judging method according to the present invention. A divergent X-ray beam 12 is emitted from an X-ray focal spot 11 of a rotating target 10 of a rotating anode X-ray tube, and it is converted into a parallel beam 16 (an incident X-ray beam) by a parabolic synthetic multilayer mirror 14, and thereafter it is incident on a sample 18. A diffracted X-ray beam 20 that has been diffracted by a sample 18 is detected by an X-ray detector 22. An angle of a diffracted X-ray beam 20 to the incident X-ray beam 16 is 2θ.

#How to use the apparatus will be described. It is assumed that the sample is a GaAs single crystal sample having a (001) plane, which is parallel to the sample surface. It is further assumed that an X-ray wavelength to be used is the wavelength (0.11957 nanometer) of the K absorption edge of Ga. First of all, the X-ray detector 22 is set at the double angle (2θ) of the Bragg angle θ of an objective crystal lattice plane that is the objective of the polarity judgment. For example, assuming that a (333) plane of the GaAs single crystal is the objective crystal lattice plane, the Bragg angle θ is 33.3 degrees at the wavelength (0.11957 nanometer) of the K absorption edge of Ga. Next, the posture of the sample 18 is adjusted so that X-rays are reflected by the objective crystal lattice plane, which is not always parallel to the crystal surface. Incidentally, since the Bragg angle θ varies with the X-ray wavelength, an expected angle position (i.e., 2θ), at which the diffracted X-ray beam is detected, of the X-ray detector 22 should vary if the X-ray wavelength varies. In other words, if the incident X-ray beam includes X-rays in a continuous wavelength range, the wavelength dependence of the intensity of diffracted X-ray beam is to be measured in a manner that the X-ray detector 22 is moved to change 2θ, and simultaneously therewith a rotation on angle ω of the sample 18 to the incident X-ray beam 16 is synchronously scanned with half an angular speed of the X-ray detector 22 (a 2θ/ω scanning).