JPH05235382A - Semiconductor device - Google Patents

Abstract

PURPOSE:To generate photoconduction for an electrical connection between a semiconductor thin film and an SrTiO3 substrate by irradiating a semiconductor device having a semiconductor thin film overlaying an SrTiO3 substrate with light having a specified range of energy at a temperature below a fixed temperature. CONSTITUTION:SrTiO3 is irradiated with a light having an energy of 3-5eV range at a low temperature below 150K to make its conductivity suddenly change and to make it have a photoconductive spectrum peculiar at a temperature if decided. Photoconductivity changes markedly in a vicinity of a temperature where SrTiO3 causes phase changes; therefore, using this SrTiO3 as a substrate to overlay it with a semiconductor thin film causes a change in the conductivity of a zone irradiated with 3-5eV ultraviolet rays to make an electrical connection with the semiconductor thin film layer in this zone, so that carriers can be injected into a semiconductor layer for example. This change can be fetched as a change in electrical characteristics of the semiconductor layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a semiconductor device provided with a substrate that produces photoconductivity against ultraviolet rays at a low temperature.

[0002]

2. Description of the Related Art A technique for electrically controlling a thin film surface of a semiconductor such as a MOS transistor is effective as a voltage control type semiconductor and a high frequency compatible type semiconductor. There is.

[0003]

For example, such a CCD
In the image sensor using, the energy gap of the semiconductor itself such as silicon which is the substrate is relatively small, so that it has high sensitivity to visible light and infrared light. Therefore, it was not possible to detect the light in the ultraviolet region having a short wavelength by distinguishing it into the light having a long wavelength such as infrared light.

On the other hand, conventionally, ultraviolet rays have been detected by using, for example, a photocell, a photocell, a phosphor, and a photographic dry plate, but utilization as a thin film active detection element is stored in, for example, a MIS type memory element. It was only used to erase the existing information. It has not even been assumed that the surface level of the semiconductor can be electrically controlled depending on the presence or absence of the irradiation of the ultraviolet rays. Furthermore, when an oxide semiconductor thin film is prepared as a conventional substrate for forming an oxide of MgO or the like, deposition is performed at a high temperature (for example, 500 ° C.), so an insulator is generated at the interface, and the substrate and the thin film are formed. There was no electrical connection between.

[0005]

According to a first aspect of the present invention, a semiconductor device having a semiconductor thin film formed on a SrTiO ₃ substrate is irradiated with light having energy in the range of 3 eV to 5 eV more than 150 K. Irradiation is performed at a low temperature to cause photoconduction, and electrical connection between the semiconductor thin film and the SrTiO ₃ substrate is possible.

According to a second aspect of the present invention, there is provided a semiconductor device in which the semiconductor thin film according to the first aspect is an oxide.

According to a third aspect of the present invention, in the oxide semiconductor thin film, at least Cu, Ti, Zn,
It contains any one metal of Sn and In, for example, Cu ₂ O, TiO ₂ , ZnO, SnO, In
O, SnInO, etc.

[0008]

The semiconductor device having the semiconductor thin film formed on the SrTiO ₃ substrate is irradiated with light having an energy in the range of 3 eV to 5 eV at a temperature lower than 150 K to cause photoconduction, and the semiconductor thin film is formed on the SrTiO ₃ substrate. Allows electrical connection between.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. S which is the substrate of the semiconductor device according to the present invention
rTiO ₃ is a paraelectric material having a perovskite structure that undergoes a structural phase transition from cubic to tetragonal. This material is tetragonal at low temperatures below about 105 K and cubic at higher temperatures.

First, the substrate sample used in the experiment was SrTiO ₃ single crystal (manufactured by Earth Jewelery Co., Ltd.) prepared by the Bernoulli method with a size width of 2.5 mm and a thickness of 0.5 mm so that the (100) face was the surface. A piece cut out with a length of 10 mm is mirror-finished on only one surface, and the electrodes are spaced at intervals of
A 5 mm thick copper wire (lead wire) fixed with a silver paste was prepared as a sample. At this time, the oxygen deficiency concentration of SrTiO ₃ is preferably 10 atomic% or less in view of characteristics.

This substrate 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 substrate 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 the sharp increase in I _Ph near the temperature at which SrTiO ₃ undergoes a structural phase transition from cubic to tetragonal is related to this transition, then the structure of the density of states changes at this time. Conceivable.

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, 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 with the light intensity. 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 temperature is determined, it has a unique photoconductivity spectrum at that temperature. I also understand. Thus, the change in the photoconductivity spectrum below 150K is
It is considered to be related to the cubic to tetragonal structural phase transition of SrTiO ₃ . Therefore, since the photoconductivity spectrum of SrTiO ₃ is significantly different between the cubic crystal state and the tetragonal crystal state, when SrTiO ₃ is used as a substrate for forming a semiconductor thin film, two types of photoconductivity spectra can be obtained.

An experimental example of a semiconductor device in which a semiconductor thin film is formed using such SrTiO ₃ as a substrate will be described. As a sample, a single crystal SrTiO ₃ (1
Cu ₂ O thin film 1000Å on the (00) surface in an oxygen atmosphere 3 ×
It was formed by a so-called reactive evaporation method in which Cu was evaporated by a resistance heating method at 10 ⁻³ Torr and a substrate temperature of 400 ° C. Then, while irradiating the light having the excitation energy of 3.4 eV, the measurement bias is set to 10 V and Cu ₂ O is used.
The temperature change of the photocurrent I _Ph flowing between the copper wires (lead wires) attached on the thin film was measured. The measurement result is shown in FIG. The figure also shows the measurement results in the case where the Cu ₂ O thin film was formed on a glass substrate as a control example.

Thus, Cu ₂ formed on the glass substrate
The O thin film, the light current _{I Ph} toward the low temperature is lowered, the sample to form a Cu ₂ O thin film SrTiO ₃ as the substrate, in the following low temperature range 150K, optical conduction SrTiO ₃ as the substrate is raised As a result (see FIG. 1), it is confirmed that the photocurrent I _Ph is increasing. This characteristically shows that electrical connection is established between SrTiO ₃ and Cu ₂ O in such a semiconductor device. In this case, Cu ₂ O conducts in the temperature range of 300 to 150 K, and SrTiO ₃ controls the conduction in the temperature range below that.

The above single crystal SrTiO ₃ (100)
TiO ₂ thin film 1000 Å on the surface 3 × 10 in oxygen atmosphere
Even when Cu is evaporated by the resistance heating method at ⁻³ Torr and the substrate temperature of 400 ° C., the same result as in FIGS. 1 to 4 is obtained due to the influence of SrTiO ₃ .

Therefore, from the characteristics shown in FIG. 1, SrTi
Since the photoconductivity changes greatly near the temperature T _{C at} which the phase transition of O ₃ occurs, when a semiconductor thin film is formed on this SrTiO ₃ as a substrate, as shown in FIG.
The conductivity of the part irradiated with 3-5 eV ultraviolet rays changes,
At that portion, an electrical connection is made with the semiconductor thin film layer, so that carriers can be injected into the semiconductor layer, for example. The change can be taken out as a change in the electrical characteristics of the semiconductor layer. Therefore, it is possible to create a photoelectric element that uses ultraviolet rays as a trigger.

From the characteristics shown in FIG. 2, the value of the temperature T _C is T _C1 , T _C2 , T depending on the intensity of the irradiation light.
_Since it changes to _C3 , it is possible to form the substrate portion of the temperature switch having different detection temperatures simply by changing the intensity of the irradiation light. Further, for example, when SrTiO ₃ is held at a temperature higher than T _C3 and irradiated with light, the state changes to a state with high conductivity (for example, the state of graph c), so that it can be used as a substrate portion of an optical switch. When the temperature is kept constant, the photocurrent value changes according to the intensity of the applied light.
The intensity of light can be measured by measuring the photocurrent value.

Further, from the characteristics shown in FIG. 3, when the temperature is changed, the photoconductivity spectrum in the ultraviolet region of 3 to 5 eV changes, and when the temperature is kept constant, the photoconductivity spectrum is determined. Can be used for a light receiving portion such as an optical switch having different light receiving characteristics.

[0023]

As described above, according to the present invention, S
A semiconductor device having a semiconductor thin film formed on an rTiO ₃ substrate is irradiated with light having an energy in the range of 3 eV to 5 eV.
By irradiating at a temperature lower than 50 K, photoconduction is caused, and the electrical connection between the semiconductor thin film and the SrTiO ₃ substrate becomes possible. Moreover, since this substrate can be grown epitaxially and is an oxide, its melting point is high and various oxide semiconductor thin films can be formed.

[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.

FIG. 4 is a graph showing a relationship between photocurrent and temperature in an example showing a semiconductor device according to the present invention.

Claims (3)

[Claims] 1. A system in which a semiconductor thin film is formed on a SrTiO ₃ substrate is irradiated with light having an energy in the range of 3 eV to 5 eV at a temperature lower than 150 K to cause photoconduction, and the semiconductor thin film and the SrTiO ₃ substrate are formed. A semiconductor device characterized in that an electrical connection between the two is possible. 2. The semiconductor device according to claim 1, wherein the semiconductor thin film is an oxide. 3. The oxide semiconductor thin film is at least Cu, T
3. The semiconductor device according to claim 2, containing any one metal of i, Zn, Sn, and In.