JPH05235383A - Photoelectric material - Google Patents

Abstract

PURPOSE:To apply SrTiO3 as a photoelectric material by irradiating SrTiO3 with light having a specified range of energy at a temperature below a fixed temperature and by generating photoconduction. CONSTITUTION:Since SrTiO3 markedly varies photoconductivity under 3-5eV ultraviolet rays at a temperature below 150K, it is applied for example as a temperature switch which detects this changed temperature. In the case of using this SrTiO3 as a substrate to manufacture a thin film by deposition at a high temperature no insulator generates in the interface between the substrate and the thin film, so that an electrical connection can be made between the substrate and the thin film and is utilized for an oxide thin film forming substrate or the like. It is doped with at least a kind of element selected from among dopable kinds of elements, that is, Nb, V, Ta or Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lw.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optoelectronic material, and more particularly to an optoelectronic material which exhibits photoconductivity with respect to light in the ultraviolet region at a low temperature of 150 K or less.

[0002]

2. Description of the Related Art Photoconductivity is a property found in a large number of substances such as solid non-metal simple substances and sulfides. For example, a photoconductive cell using CdS is a photosensitive part of a light switch or an optical amplifier part. It is used for the element and so on. The photoconductive element is characterized in that it has high sensitivity to infrared rays having a wavelength longer than the limit wavelength of the external photoelectric effect.

On the other hand, semiconductor materials such as silicon and germanium, which have a relatively small energy gap, are also used as photoelectric materials, and these have high sensitivity to visible light and infrared light. It is characterized in that it can be used for thinning.

[0004]

However, these photoelectric materials that have been conventionally used are photoelectric materials that cannot be used in the ultraviolet region because they mainly utilize the spectral characteristics for visible light or infrared light. Moreover, when a conventional photoelectric material is used as a substrate and a thin film is formed on the substrate by deposition at a high temperature (for example, 500 ° C.), an insulator is generated at the interface between the substrate and the substrate, Electrical connection between the membrane and the membrane could not be made.

Further, the conventional photoelectric material is ideally preferably handled at a place having a constant ambient temperature because of its temperature drift characteristic, and it is general to compensate so as to suppress the temperature drift. However, there is no photoelectric material that positively utilizes the change in the photoconductive property due to the temperature change as the electric property. Furthermore, no photoelectric material in a low temperature region of 150 K or less has been reported.

[0006]

Therefore, the present inventors have
Studies on the structural phase transition have been conducted already (for example, RO Bell and G. Ru.
pprecht, Phys. Rev. 129 (196
3) 90), a new application technique for SrTiO _3, which has not been considered as a photoelectric material at all because it is an electrical insulator, has been newly found.

That is, the material according to the present invention is to apply light having energy in the range of 3 eV to 5 eV at a temperature lower than 150 K to apply SrTiO ₃ which causes photoconduction, as a photoelectric material.

[0008]

The function of SrTiO ₃ is 3-5 eV of ultraviolet light.
Since the photoconductivity changes greatly at temperatures lower than 150K,
For example, it is used as a temperature switch that detects this change temperature. Further, when this SrTiO ₃ is used as a substrate and a thin film is formed on it by deposition at a high temperature, an insulator does not occur at the interface between the substrate and the thin film, so that the electrical property between the substrate and the thin film is It can be connected and is used as a substrate for oxide thin film formation.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. SrTiO 3 which is a photoelectric material according to the present invention
Reference numeral ₃ is a paraelectric material having a perovskite structure that undergoes a structural phase transition from cubic to tetragonal. This material is about 105K
It becomes tetragonal at the following low temperatures and becomes cubic at higher temperatures.

Experimental examples of this substance will be described below. First, the sample used in the experiment was made of SrTiO ₃ single crystal (manufactured by Earth Jewelery Co., Ltd.) prepared by the Bernoulli method with a size width of 2.5 so that the (100) face was the surface.
A sample cut out with a thickness of 0.5 mm, a thickness of 0.5 mm and a length of 10 mm was mirror-finished on only one side, and electrodes were prepared by fixing copper wires with a silver paste at an interval of 1.5 mm as a sample. At this time, the oxygen deficiency concentration of SrTiO ₃ is preferably 10 atomic% or less in view of characteristics.

This sample was placed on a copper base of a refrigerator and evacuated to 10 mTorr by a rotary pump. After that, the sample was spectrally separated by a 500 W Xe lamp with a monochromator. The temperature of the sample was lowered while irradiating light having an excitation energy of 3.35 eV through the sapphire window. During this time, the temperature of the sample was monitored with a thermocouple attached with silver paste.

FIG. 1 shows the temperature dependence of the photocurrent I _{Ph with} respect to the excitation light of 3.35 eV.
The photoconductivity rapidly increases exponentially toward a low temperature near 20 to 100K. Here, 105K is SrTi
It is a structural phase transition temperature of O ₃ , and it is known that a cubic crystal is formed at a temperature higher than that and a tetragonal crystal is formed at a temperature lower than that.
The rapid increase in photoconductivity seen here has never been reported before. In addition, the characteristic of FIG. 1 takes the same locus in the case where the temperature is gradually reduced and the temperature is gradually increased, and no hysteresis is observed.

Thus, if a sharp increase in I _Ph near the temperature at which SrTiO ₃ undergoes a cubic to tetragonal structural phase transition is related to this transition, then the structure of the density of states changes at this time. It is thought that

Next, in the characteristics shown in FIG. 1, changes in the characteristics due to the intensity of the irradiation light were measured. The measurement result is shown in FIG. In FIG. 2, graph a,
In b and c, the relative intensity of light to be irradiated is 1.0, 0.
This is the case of 1,0.01. From the figure, T _C1 , T _C2 ,
If T _C3 is defined as, for example, the temperature of 10% of the photocurrent value after the transition on the I _Ph (T) curve, 115 K, respectively.
It becomes 111K and 104K. Although increasing the light intensity may raise the temperature of the sample slightly, the increase in T _C here is not considered to be a thermal effect. Thus, it is expected that when the light intensity is increased, the transition temperature gradually increases as the light intensity increases. It is considered that this is because the formation of electron-hole pairs by absorption of photons affects the SrTiO ₃ phase transition.

Further, the change in the photoconductivity spectrum when the temperature was changed was measured. The measurement result is shown in FIG. In FIG. 3, 110K, 113K, 123K,
It shows measurements in the UV region of 3-5 eV at a temperature of 142K. The measured values at the temperature of the former two are values in the unit (μA) shown on the left axis in FIG. 2, and the measured values at the temperature of the latter two are values in the unit (nA) shown on the right axis.

From the above measurement results of FIGS. 1 to 3, 3
By irradiating SrTiO ₃ with light having an energy in the range of ˜5 eV at a temperature lower than 150 K or lower, its conductivity changes rapidly and, if the ambient temperature is determined, it has a photoconductivity spectrum specific to that temperature I understand.
It is considered that such a change in the photoconductivity spectrum at 150 K or less is related to the structural phase transition of SrTiO ₃ from cubic to tetragonal.

It should be noted that the above-mentioned value of 150K is the measurement result of FIGS. 1 to 3 and various elements that can be doped, that is, the group of Nb, V, Ta or Sc, Y, La, C.
e, Pr, Nd, Pm, Sm, Eu, Gd, Tb, D
The value is regulated from an experimental example when at least one element selected from y, Ho, Er, Tm, Yb, and Lu is doped (in particular, the doping rate is 5 atomic% or less). Moreover, an N-type or P-type photoelectric material can be obtained by such doping.

[0018]

As described above, according to the present invention, 3
Since the photoconductivity greatly changes at a temperature lower than 150 K for an ultraviolet light of up to 5 eV, if the ultraviolet light is kept constant, it can be used as a temperature switch for detecting a temperature of 150 K or lower. On the contrary, when the temperature is kept constant, the photoconductivity spectrum peculiar to the temperature is determined, so that it can be used for an optical modulator, an optical oscillating device, etc. using ultraviolet light of 3 to 5 eV. Furthermore, when this SrTiO ₃ is used as a substrate and a thin film is formed on this by deposition at a high temperature, epitaxial growth is possible and SrTiO ₃ is an oxide with a high melting point. It can be used as a substrate for forming an oxide thin film or the like, which does not generate an insulator and can make an electrical connection between the substrate and the thin film.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between photocurrent and temperature for SrTiO ₃ .

FIG. 2 is a graph showing the relationship between the photocurrent and the temperature of SrTiO ₃ depending on the intensity of the irradiation light.

FIG. 3 is a graph showing changes in photoconductivity spectrum of SrTiO ₃ when temperature is changed.

Claims (6)

[Claims] 1. A photoelectric material characterized by irradiating SrTiO ₃ with light having an energy in the range of 3 eV to 5 eV at a temperature lower than 150 K to cause photoconduction. 2. The photoelectric material according to claim 1, which is doped with at least one element selected from the group consisting of Nb, V and Ta. 3. The photoelectric material according to claim 2, wherein the doping ratio is 5 atomic% or less. 4. Sc, Y, La, Ce, Pr, Nd, P
m, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
The photoelectric material according to claim 1, which is doped with at least one element selected from the group consisting of m, Yb, and Lu. 5. The photoelectric material according to claim 4, wherein the doping rate is 5 atomic% or less. 6. The photoelectric material according to claim 1, wherein the oxygen deficiency concentration of SrTiO ₃ is 10 atomic% or less.