JPS6363946A - Cryostat for spectrometry - Google Patents

Abstract

PURPOSE:To remove measuring noises caused by bubbles generated from a cryogen during the measurement, by setting a sample chamber on the side of a cryostat body while a sample base as heat good conductor is provided in the sample chamber. CONSTITUTION:A cryostat body 11 is filled with a liquid nitrogen 103 as refrigerant. A sample chamber 12 sticks out horizontally from the side of the body 11. A copper sample base 13 as heat good conductor having a sample 105 thereon is inserted into the sample chamber 12. Without the sample base 13, the sample chamber 12 will not be cooled as exposed to radiation heat from outside. The horizontal layout of the sample 105 eliminates the need for a specified fixed means. Furthermore, as the sample chamber 12 is of a lateral type, a passage 14 of a vapor gas is formed in the sample 105 so constant as to generate bubbles 113 only on the side of the body 11. Thus, there is no bubble intercepting the optical path of the excitation light 15 intermittently thereby eliminating noises during the measurement.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention relates to a sample cooling device used for low-temperature spectroscopic measurements of solid samples, which is widely used as a method for evaluating the physical properties of semiconductor crystals. This invention relates to a cryostat for spectrometry.

(Prior art) When developing and manufacturing semiconductor devices, spectroscopic measurements are widely used as a method for evaluating semiconductor crystals, which are the constituent materials of the devices, as they are relatively simple, highly accurate, and provide a large amount of information1. ,
The quality of the characteristics of a semiconductor laser device manufactured by growing multiple Al2GaAs crystalline layers on a GaAs single crystal substrate is determined by:
Since the quality largely depends on the quality of the grown A12GaAs crystal, photoluminescence measurement, which is one of the spectroscopic measurements, is used as a crystal evaluation method. An example of this photoluminescence measurement will be described below.

The schematic configuration of the photoluminescence measuring device is shown in FIG. That is, when excitation light from a light source 21 such as a discharge tube or a gas laser is focused by a lens 22 and irradiated onto a sample 24 cooled within a cryostat 23, fluorescence is emitted from the sample. Lens 2
5, the light is collected and introduced into a spectrometer 26, and the light is dispersed into a detector 27,
The photoluminescence spectrum (
A fluorescence spectrum due to optical excitation) is obtained. Sample 2 above
4, when measuring a GaAs single crystal, the light source 21 is usually an argon ion laser, the spectrometer 26 is a visible/near-infrared spectrometer, and the detector 27 is a photomultiplier tube.

A GaAs single crystal, which is a sample, is placed in a cryostat 23 and is often cooled with a cryogen. The reasons for this are: firstly, cooling the sample allows for stronger fluorescence and easier measurement; secondly, the shape of the measured photoluminescence spectrum becomes sharper and 1131 fine structures can be measured, making it easier to analyze in detail. This is something that can be done.

Next, the cryostat 23 that cools the sample 24 has various types depending on the cryogen and cooling method, but the one that is simple and has good temperature accuracy is one made of hard glass or quartz glass, as shown in Figure 3. Sample chamber 101 at the bottom
A cryostat body 102 equipped with a cryostat is filled with a cryogen such as liquid nitrogen 103, and a sample 105 is placed in a sample cylinder 104 disposed in the sample chamber and immersed in the cryogen. The sample 105, which is so-called "Jiyabu pickled", is irradiated with excitation light 106 and the fluorescence emitted from the sample is spectroscopically measured to obtain a photoluminescence spectrum at liquid nitrogen temperature. Compared to measuring at room temperature without cooling the sample, the fluorescence intensity is 50~
It is 100 times stronger and the spectral width is sharper than 172,
This is important information for determining the crystallinity of the sample.

By the way, using liquid helium as a cryogen requires a double thermos flask for the cryostat, and liquid helium is expensive, so it is difficult to use on a regular basis and is not convenient. In indirect cooling methods, the temperature of the sample does not completely drop to the temperature of the cryogen, and the sample is heated by irradiation with strong excitation light, resulting in temperature unevenness and temperature rise within the sample. Controlling the sample temperature with good reproducibility is difficult and cannot be done regularly.

Because of the above-mentioned reasons, the method of soaking with a cryostat shown in FIG. 3 is widely used as a simple and accurate method for setting the sample temperature.

However, the cryostat shown in FIG. 3 has three major problems as described below. First, the liquid nitrogen used as a cryogen constantly boils and bubbles, and the bubbles 113 passing through the optical path of the excitation light and fluorescence become a source of noise during measurement. Second, since samples are generally irregular in shape and size and are easily broken, the sample 105 is placed on the sample stand 10.
4. There is no simple and reliable method for fixing. Thirdly, the sample chamber 101 is connected to the cryostat main body 102.
Because it is located at the bottom of the camera, it is not possible to use the so-called microspectroscopy method, which involves setting the excitation light irradiation position under a microscope and performing spectroscopic measurements at a predetermined position. It is time consuming.

(Problems to be Solved by the Invention) This invention eliminates the noise that occurs during measurement due to the bubbles generated by a cryogen, such as liquid nitrogen, which is a problem in cryostats for spectroscopic measurements, and also provides simple and stable sample holding. This makes it possible to perform spectroscopic measurements under a microscope.

[Structure of the Invention] (Means for Solving Problems) A cryostat for spectrometry according to the present invention is a cryostat for spectrometry that directly cools a sample placed in a sample chamber with a liquid cryogen, in which the sample chamber is connected to the cryostat main body. The sample table is installed on the side of the sample chamber, and is equipped with a sample stage made of a good thermal conductor, which prevents measurement noise caused by foam generated from cryogen, liquid nitrogen, etc., during measurement. do.

(Function) In the cryostat according to the present invention, liquid nitrogen as a cryogen flows into the horizontal sample chamber along the sample stage, and immerses the sample placed horizontally on the sample stage, resulting in "jiyabuzuke". Since the sample is placed horizontally, no special fixing means are required. In addition, since the sample chamber is horizontal, the gas from the vaporized cryogen in the sample chamber connects with the cryostat when it moves toward the cryostat body.
A flow path for vaporized gas in the sample chamber is constantly formed. Therefore, since there are no air bubbles that intermittently block the optical path near the sample, no noise occurs during spectroscopic measurements. Furthermore, since the sample chamber has a structure that protrudes from the side of the cryostat body, it is possible to perform microscopic side illumination, which can be determined by installing the cryostat under a normal microscope and checking the irradiation position of the excitation light. All three problems mentioned above that were unavoidable with conventional cryostat are solved.

(Example) An example of the present invention will be described below with reference to FIG. In addition, in the description, parts that are the same as in the prior art are indicated by the same reference numerals as in the prior art in the drawings, and the description thereof will be omitted.

The cryostat main body 11 in FIG. 1 is a thermos made of quartz glass similar to the conventional one, and is filled with liquid nitrogen 103 as a cryogen. The sample chamber 12 projects horizontally from the side surface of the cryostat main body 11. A copper sample stage 13 on which a sample 105 is placed is inserted into the sample chamber 12 . The sample stage 13 has two functions.

The first is that the cryogen liquid nitrogen 103 does not collapse the inside of the sample chamber 12 until the sample stage 13 made of a good thermal conductor such as copper or aluminum is inserted into the sample chamber 12. The sample chamber 12 is not coated with heat-shielding plating to perform spectroscopic measurements, so without the sample stage 13, the sample chamber 12 will not be cooled by radiant heat from the outside world, and even if liquid nitrogen flows in. It vaporizes immediately, and the inside of the sample chamber 12 is not crushed. Furthermore, a flow path 14 for vaporized nitrogen gas is constantly formed above the sample 105, and bubbles 113 are formed on the cryostat main body side, so there are no bubbles that intermittently block the optical path of the excitation light 15, and during measurement. Noise disappears.

The second is to fix the sample 105 on the sample stage 13. However, instead of fixing the sample vertically as in the conventional case, the sample was simply held horizontally, and no special work was required, and in this example, the copper piece was simply bent. The dimensions of the cryostat of this example are such that the cryostat main body has an outer diameter of 60 nm, the sample chamber has an inner diameter of 5 m, and a length of 30 m, which is large enough to fit on a microscope stage for microscopic spectroscopy.

Liquid nitrogen temperature (
In the photoluminescence measurement at 77K), the noise caused by the bubbles of the vaporized gas of the cryogen, which was the case in the past, was not affected by all <aX, and the measurement was successful. The obtained spectrum correctly showed the peak energy and half-width at the liquid nitrogen temperature, confirming that the sample was "soaked" in liquid nitrogen and that the sample temperature matched the cryogen temperature. . Furthermore, the measurement time (even if it is difficult, the troublesome work of aligning the optical axis can be significantly reduced, and the measurement can be performed in about 173 seconds compared to the conventional method. In addition, so-called microscopic spectroscopy under a microscope can be easily performed. was completed.

Although quartz glass was used as the material for the cryostat in this embodiment, it is clear that a structure in accordance with the gist of the present invention can be obtained even if hard glass or metal is used. Further, although copper was used as the material for the sample stage, other materials can be used as long as they are good thermal conductors. Next, photoluminescence measurements were performed as an example of spectroscopic measurements, but the cryostat of the present invention can also be used for spectroscopic measurements such as Raman scattering, photoconduction, and optical reflection/absorption. Also, although liquid nitrogen was used as the cryogen, other liquid cryogens can be used to change the temperature.

〔Effect of the invention〕

According to the cryostat according to the present invention, although the sample is "jiyabuke" in the cryogen, it is not affected by the bubbles of the vaporized cryogen and requires a simple sample fixation method, which is simple, quick, and temperature-controlled. Highly accurate and noise-free spectroscopic measurements are now possible. Furthermore, microscopic spectroscopy has become easier.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an embodiment of a cryostat for spectrometry according to the present invention, Fig. 2 is a schematic diagram of the configuration of a photoluminescence measurement device as an example of spectrometry, and Fig. 3 is a conventional cryostat for spectrometry. FIG. 11... Cryostat main body 12... Sample chamber 13... Sample stage 14.
...Nitrogen gas flow path 15...Excitation light 103...
cryogen

Claims (1)

[Claims] In a cryostat for spectrometry that directly cools a sample placed in a sample chamber with a liquid cryogen, the sample chamber is installed on the side of the cryostat body, and the sample chamber is equipped with a sample stage made of a good thermal conductor. A cryostat for spectroscopic measurements.