1. IntroductionWith the progress in semiconductor industry,

diversification of electronic materials has been ad-vancing from Si, which once played a central role, tocompound semiconductors, and further to thin filmmaterials which are products of epitaxial growth onsemiconductor substrates. In parallel with this trend,ever more importance is being given to evaluation ofmonocrystalline materials by X-ray diffraction tech-niques.

The TRIAX goniometer is so designed that itincorporates both the function of a wide angle gonio-meter and that of a bar system fine rotation gonio-meter; these two goniometers have been used in acomplementary manner according to the purpose ofmeasurement. The TRIAX consists of three coaxialrotation axes of a unique design, such that it allows torotation of the sample stage by means of two shafts for fine and coarse rotations, in addition to 2θ rotation forthe X-ray detector. An upgraded system with this

goniometer can cope with diffractometry for all sortsof monocrystals.

2. Construction of the TRIAX GoniometerFig. 1 shows the axial construction of the TRIAX

Goniometer. The salient feature is that the ei ro­tationcan be performed in two ways, coarse and finerotations. The coarse rotation is made by the wormand worm wheel, as in the case of the conventionalwide angle goniometer, over 360° in 1/1000° steps.But there is a difference in that the worm shaft is fixedto another rotation shaft, the ω fine shaft, whichpermits rotation by a bar system fine rotationmechanism. This mechanism is such that a steel ballburied in the tip of a bar extended from the rotationshaft is held by the end surface of a micrometerspindle, and that the steel ball is pushed from theopposite side by a pressing spring. The amount ofdisplacement of the micrometer is then converted to afine angular rotation. This device is known as a sinebar system fine rotation mechanism.

30 The Rigaku Journal

The Rigaku Journal

Vol. 5/ No. 1/1988

Product Information

TRIAX GONIOMETERFOR MONOCRYSTAL X-RAY DIFFRACTOMETRY

3. Examples of Systems using the TRIAXGoniometerSuperlattice Periodic Structure Measuring SystemSLX- 1

Recently, semiconductor heterostructure super-lattices are drawing attention by being applied to highelectron mobility transistors (HEMT) or quantum-well lasers. The captioned system is designed forassessment and analysis of the periodic structure ofsuch semiconductor superlattices by measuring thesmall angle scattering, satellite reflection and rockingcurve with X-rays. (Fig. 2)

The X-ray optical system, when built up on asingle cast-iron surface plate, permits monochro-matic (or direct) beam diffractometry and the doublecrystal method rocking curve measurement.

The monochromator for use is not limited to a flat plate type. It is also possible to assemble the X-rayoptical system by the use of a channel cut crystal. Itmay be possible, furthermore, to arrange pluralmonochromator crystals in an exchangeable way toallow switchover of the optical system by one­touchoperation.

Vol. 5 No. 1 1988 31

Fig. 1 Construction of TRIAX goniometer.

32 The Rigaku Journal

Fig. 2 System block diagram.

Fig. 3 Small angle scattering profile of multilayer film.

Measurement Examples

A) Small angle scattering

A small angle scattering pattern of W/Si multilayerfilm used for soft X-ray spectral work. (Fig. 3)

The beam monochromated by a Ge (220) mono-chromator is made to be incident on the sample.

Total reflection profiles at low angles as well aslong-periodicity reflections of up to the 2nd order canbe observed.

Vol. 5 No. 1 1988 33

Fig. 4 Diffraction profile of semiconductor superlattices.

Fig. 5 Rocking curve.

B) Profile by wide angle diffractometry

A diffraction profile obtained from semi-conductor superiattices of InP/GaAs composed on aInP substrate. (Fig. 4)

Observable are Bragg reflections from thesubstrate, the 0th-order peak which gives a mean

lattice, constant for superlattices, and ±lst-ordersatellite reflections.

A Si (111) monochromator was used.

C) Rocking curve obtained by the double crystal method with (+,-) parallel setting

A rocking curve obtained from InGaAsPmono crystalline thin film which was produced byepi taxial growth on a InP substrate. (Fig. 5)

Lattice missmatching ∆d/d of the epitaxial layerwith respect to the substrate can be obtained through

the difference in peak position ∆θ between the sub-strate and the epitaxial layer. Besides, oscil lationsseen in the profile were caused by X-ray interference(Pendellösung Fringes). The period ∆ω reflects thefilm thickness.