JP2005055307A - Method and apparatus for measuring level in forbidden band by photoluminescence with added thermal excitation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for measuring a level in a forbidden band by photoluminescence with added thermal excitation which conveniently and accurately measure energy of the level in the forbidden band such as a trap level. <P>SOLUTION: A light emitted by an electron or a hole released from the trap level is observed and the energy of the level in the forbidden band is nondestructively, noncontactly, conveniently and surely separated and measured by organically combining an excitation light of an energy width of the forbidden band of materials or more, an excitation light of the energy width of the forbidden band of the materials or less and thermal energy when the emitted light, the received light and the level in the forbidden band in the electronic material are quantitatively measured. A factor for generating the level in the forbidden band is clearly expressed. A material composition, a manufacturing process and a device structure are easily optimized through a removal of the factor and the efficiency of a light emission/display device is improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is present in light-emitting / light-receiving and electronic materials, and in order to lower the device efficiency, stability and reliability, it is desired to elucidate the cause and eliminate the level in the forbidden band (such as defects and residual impurities). Non-destructive, non-contact optical measurement method and its measurement to detect and evaluate with high accuracy the energy level that should not be inherent, which acts as a trap level or non-radiative recombination level. It relates to the device.

  In conventional photoluminescence (PL), it is easy to obtain the relative ratio of emission intensity between different samples, but the non-emission recombination levels and trap levels that determine device efficiency, stability, and reliability. It was impossible to examine the behavior quantitatively.

  On the other hand, the inventors of the present invention have two-wavelength excitation PL of excitation light (Above-Gap Excitation, AGE) that is greater than or equal to the forbidden band energy width and excitation light (Below-Gap Excitation, BGE) that is less than or equal to the forbidden band energy width. The method showed that non-radiative recombination parameters such as the energy, spatial distribution, concentration, and electron / hole capture rate of the forbidden band level acting as a non-radiative recombination level can be derived quantitatively. . In addition, it was shown that the non-radiative recombination parameters can be derived more easily from the time-resolved PL response by pulse excitation (see Patent Document 1 below).

  However, the energy distribution of the non-radiative recombination level can be measured here by changing the BGE energy. However, in practice, it is necessary to prepare a light source with sufficient intensity up to the infrared region. It is not so easy to measure.

  In addition to this, there is a method (thermoluminescence method) in which light is emitted as a function of temperature while trapping carriers at a trap level and then raising the temperature at a constant rate while raising the temperature.

In this method, if the measurement is performed multiple times while changing the heating rate, the energy of the trap level is required, but the measurement takes time and the accuracy is not sufficient, and other non-radiative recombination levels. Could not be separated.
JP 2002-286640 A (page 2-3, FIG. 2) E. Kanoh, K .; Hoshino, N .; Kamata, K .; Yamada, M .; Nishioka and Y.J. Arakawa, J .; Lumin, 63, pp. 235-240, 1995. N. Kamata, J .; M.M. Z. Ocampo, K.M. Hoshino, K .; Yamada, M .; Nishioka, T .; Someya and Y.M. Arakawa, Recent Res. Developments in Quantum Electronics, 1, pp. 123-135, 1999.

  Non-destructive and non-contact measurement methods from the industry to detect and evaluate forbidden band levels with high accuracy in order to improve element efficiency, stability, and reliability of light emitting / receiving and electronic materials / devices It is strongly desired.

  In view of the above situation, the present invention measures the level in the forbidden band by photoluminescence with thermal excitation that can easily and accurately measure the energy in the forbidden band level including the trap level. It is an object to provide a method and a measuring device thereof.

In order to achieve the above object, the present invention provides
[1] In the method for measuring the level in the forbidden band by photoluminescence (PL) with thermal excitation,
(A) Light emission / light reception and electronic material are irradiated with AGE light or BGE light of photon energy E _exc beforehand at a low temperature so that excited carriers (electrons or holes) are trapped in the trap level in the forbidden band,
(B) After blocking the AGE light or the BGE light, the photon energy at a certain intermediate temperature when observing the light emission by the carriers thermally released from the trap level as a function of temperature while increasing the temperature at a constant temperature rising rate. by irradiating BGE light E _B, and photoexcitation by BGE the trap level of the carriers then have to irradiate heat radiated by will will capture energy E _T <E _B, to produce a light emission at a time, this At a later temperature rise, no carriers are present at the trapping level of trapping energy E _T <E _B , so no light emission occurs, and the carrier reaches a temperature at which the carriers from the level of trapping energy E _T > E _B are thermally released. For the first time,
(C) From the reciprocal relationship between photoexcitation and thermal excitation, the energy of the level in the forbidden band is detected using specific photon energies E _exc and E _B or a combination of different E _exc and E _B. It is characterized by doing.

Here, for simplification, a semiconductor having two trap levels (energy E _T1 and E _T2 ) and one non-radiative recombination level (energy E _NT ) is illustrated in FIG. The process will be described.

Figure 1 shows the energy band diagram of a semiconductor with two trap levels (energy E _T1 and E _T2 ) and one non-radiative recombination level (energy E _NT ) (think only electrons for simplicity). It is. Here, in (a) above, electrons are trapped in the trap levels 1 and 2 by the AGE light. In this case, in normal thermoluminescence measurement, electron emission from the trap level 1 to the non-radiative recombination level and the conduction band (required energy ΔE ₁ = E _NT −E _T1 , ΔE ₂ = E _g −E _T1 ) Although it occurs at temperatures T ₁ and T ₂ (T ₂ > T ₁ ), only the emission process at temperature T ₂ is observed as light emission. At this time, the electron emission from the trap level 2 is not observed because the temperatures corresponding to ΔE ₃ = E _NT −E _T2 and ΔE ₄ = E _g −E _T2 are too high, and eventually the trap level 2 and the non-radiative recombination The level is not detected.

On the other hand, when the temperature is raised to the above-described temperature T ₂ in (b), the electrons at the trap level 1 are already emitted as shown in FIG. 2, and the electrons are captured only at the trap level 2. ing. When the temperature is maintained in this state and irradiation with BGE light having photon energy E _B2 = E _g −E _T2 is performed, electron emission from the trap level 2 to the conduction band is observed as light emission. In addition, after electron capture with AGE light again and temperature rise to T ₂ , this time, instead of E _B2 , first irradiate BGE light of E _B1 = E _NT −E _T2 , and then BGE light of the previous E _B2 , The electrons in the trap level 2 are non-radiatively recombined via the non-radiative recombination level, and thus no light emission occurs (see FIG. 2).

From this, it is possible to quantitatively detect the energy of the trap level 2 and the non-radiative recombination level that could not be measured by the conventional method. As shown in FIG. 3, when BGE light having photon energy E _exc = E _T2 is first used instead of AGE light, electrons can be captured only at the direct capture level 2. Therefore, the capture level and the non-radiative recombination level in the forbidden band are individually determined by the combination of the photon energy E _exc that captures carriers to the capture level and the photon energy E _B that releases carriers from the capture level as described above. In addition, it is possible to quantitatively measure the individual.

[2] In a forbidden band level measuring device using photoluminescence (PL) with thermal excitation, it acts on an AGE light source that emits AGE light, a BGE light source that emits BGE light, and a luminescent material as a sample a cooling and heating device, a temperature control device for controlling the temperature of the cooling and heating device, and a sensor for detecting the temperature of the sample, AGE light pre photon energy E _exc at a low temperature in the light emitting and receiving and electronic materials Or, by irradiating with BGE light, the excited carriers (electrons or holes) are trapped in the trap level in the forbidden band, and after blocking the AGE light, the temperature control device is used to raise the temperature at a constant heating rate. , when observing light emitted by carriers heat released from the trap level as a function of temperature, is irradiated with BGE light of photon energy E _B at some intermediate temperatures, unless irradiated The trap level of a carrier of heat emitted will capture energy E _T <E _B is photoexcited by BGE after, the light emission caused at a time, a Atsushi Nobori after this, capture energy E _T <the E _B Since there is no carrier in the trap level, no light emission occurs, and the next light emission is generated only when the carrier from the level of the trap energy E _T > E _B reaches the temperature at which heat is released. From the reciprocal relationship, the energy of the level in the forbidden band is measured using specific photon energies E _exc and E _B , or a combination of a plurality of different E _exc and E _B.

  According to the present invention, the following effects can be achieved.

  (A) Non-destructive and non-contact optical measurement, and since no electrode is required, measurement and evaluation can be performed for each process regardless of the sample shape.

  (B) Local evaluation is possible by reducing the excitation light spot size. As this limit, it is possible to measure single molecules and single quantum dots using near-field optical technology. On the other hand, when the spot size is increased, average information of a wide area can be easily obtained.

  (C) Level energy and spatial distribution measurement by light emission observation can be easily performed in a wider energy range.

  (D) Information on non-radiative recombination levels other than the trap level cannot be obtained by conventional thermoluminescence measurement, but this is possible in the present invention. As a result, the forbidden band level can be comprehensively evaluated.

  (E) The measurement time, which is a problem in thermoluminescence measurement, can be greatly shortened and the measurement accuracy can be improved.

Light emission, light reception, and electronic material are preliminarily irradiated with AGE light or BGE light with photon energy E _exc at a low temperature, and excited carriers (electrons or holes) are captured in a trap level in the forbidden band. After blocking the AGE light or BGE light, light emission from the carriers thermally released from the trap level is observed as a function of temperature while the temperature is increased at a constant temperature increase rate. At this time, when the BGE light having the photon energy E _B is irradiated at a certain intermediate temperature, the carriers in the trap level E _T <E _B that would have been thermally radiated if not irradiated are photoexcited by the BGE at a time. Luminescence occurs. At the subsequent temperature rise, no carriers are present at the trapping level of trapping energy E _T <E _B , so no light emission occurs, and the temperature reaches the temperature at which carriers from the level of trapping energy E _T > E _B are thermally released. The next light emission occurs for the first time.

Due to the reciprocal relationship between photoexcitation and thermal excitation, the present invention utilizes specific photon energies E _exc and E _B , or a combination of a plurality of different E _exc and E _B , so Easily and reliably measure the energy of the luminescence recombination level. In addition, this measurement technique and a measurement apparatus capable of performing two-wavelength excitation luminescence measurement while keeping the sample at a constant temperature and raising the temperature at a constant speed are provided.

  FIG. 4 is a block diagram of an apparatus (system) for measuring levels in the forbidden band by photoluminescence with thermal excitation according to an embodiment of the present invention.

  In this figure, 1 is an AGE light source, 2 is a BGE light source, 3 is a sample, 4 is a spectrometer, 5 is a photomultiplier tube, 6 is a digital oscilloscope, 7 is a boxcar integrator, 8 is a computer, 9 is cooling and A heating device, 10 is a temperature control device, and 11 is a temperature sensor.

  For example, when GaN, which is a blue light emitting semiconductor, is evaluated as the sample 3, the AGE light source 1 is a combination of a deuterium lamp and an interference filter, the BGE light source 2 is a continuous wave Nd: YAG laser, or a wavelength-tunable laser. Pulsed lasers such as an Nd: YAG laser excitation light parametric oscillator (OPO), a dye laser, and a Ti: sapphire laser are used. The light emitted from the sample 3 is separated by the spectroscope 4 and then received by the photomultiplier tube 5, and the time response waveform (in the case of continuous wave laser excitation, the waveform change due to the intermittent chopper) is a digital oscilloscope 6 or box. It is recorded in the computer 8 through the Kerr integrator 7 or the like. Further, the computer 8 is connected to the AGE light source 1 or the BGE light source 2 so as to obtain these excitation lights.

  Further, the present invention has a configuration for controlling the temperature of the sample 3. That is, a cooling and heating device 9 that acts on the sample 3, a temperature control device 10 that controls the temperature of the cooling and heating device 9, and a temperature sensor 11 that detects the temperature of the sample 3 are provided.

  Hereinafter, an embodiment of the measurement of energy in the forbidden band level by photoluminescence with thermal excitation according to the present invention will be described.

  FIG. 5 is a diagram showing the temperature dependence of the emission intensity when the BGE irradiation according to the present invention is applied, and FIG. 6 shows the temperature dependence of the emission intensity when the BGE irradiation according to the present invention is not applied and each peak. It is a figure which shows the energy of the capture level to bring.

Y ₂ O ₂ S: Eu ³⁺ is known as a standard red phosphor. Therefore, when photoexcitation of Y ₂ O ₂ S crystal maternal excited carriers moved to Eu ^3+, resulting in specific red emission (wavelength 626 nm) by f-f transition of Eu ^3+. This Y ₂ O ₂ S: Eu ³⁺ phosphor (4.5 mol%) is cooled to 15 K and irradiated with AGE light having a wavelength of 240 nm (photon energy E _exc = 5.17 eV) at an intensity of 0.25 nW / mm ² for 300 seconds. And the capture level in the forbidden band was filled with the carrier.

Next, the temperature was increased to 60 K at a rate of 3.17 K / min (K / min), and BGE light having a wavelength of 1064 nm (photon energy E _B = 1.17 eV) was irradiated at an intensity of 7.87 mW / mm ² . As shown in FIG. 5, a temporary increase in emission intensity due to Eu ³⁺ f-f transition was observed. Thereafter, while continuing the BGE irradiation, the temperature was raised at a rate of 3.17 K / min (K / min) and the emission intensity was examined as a function of temperature, and the following peak was observed at around 260 K.

On the other hand, the same sample is cooled to 15 K, and AGE light with a wavelength of 240 nm (photon energy E _exc = 5.17 eV) is irradiated for 300 sec at an intensity of 0.25 nW / mm ² to fill the trap level in the forbidden band with carriers. It was.

Next, when the temperature was raised to 300 K at a rate of 3.17 K / min (K / min), at least six emission peaks were observed. As shown in FIG. 6, paying attention to four emission peaks from the low temperature side among these, energy required for carrier emission accompanied by light emission from the trap level that causes them (ΔE ₂ = E at the trap level 1 in FIG. 1). _g− E _T1 , the energy corresponding to ΔE ₄ = E _g −E _T2 in the trap level of FIG. 2) is ε ₁ , ε ₂ , ε ₃ , ε _4, and these values are expressed as β ₁ , Β ₂ was obtained from the peak temperatures T _m1 and T _{m2 in} the two-stage measurement. As a result, ε ₁ = 0.22 eV (T _m1 = 62.8 K, T _m2 = 53.7 K, β ₁ = 13 K / min, β ₂ = 0.36 K / min), ε ₂ = 0.55 eV (T _{m1 = 107.4K, T m2 = 98.1K} , β 1 = 9.0K / min, β 2 = 0.5K / min), ε 3 = 0.69eV (T m1 = 132.9K, T m2 = 121 .6K, β ₁ = 9.0 K / min, β ₂ = 0.5 K / min), ε ₄ = 1.10 eV (T _m1 = 192.9 K, T _m2 = 179.7 K, β ₁ = 4.0 K / min, β ₂ = 0.33 K / min).

Here, when FIG. 5 irradiated with BGE light (photon energy E _B = 1.17 eV) after heating up to 60 K is compared with FIG. 6 without irradiation, the emission peak ε ₂ (0.55 eV in FIG. 6) is compared. ), Ε ₃ (0.69 eV) and ε ₄ (1.10 eV) are not detected in FIG. This is because the photon energy E _B of the BGE light irradiated in FIG. 5 is 1.17 eV (> ε ₂ , ε ₃ , ε ₄ ), resulting in emission peaks indicated by ε ₂ , ε ₃ , ε ₄ in FIG. This is because the trap level releases all the carriers by this BGE irradiation, and even if sufficient thermal energy is obtained by the subsequent temperature increase, carrier emission no longer occurs. In addition, since an emission peak near 260 K is obtained in FIG. 5, it is found that the carrier emission energy at the trap level that causes this emission peak is 1.17 eV or more.

  That is, the photon energy of the BGE light irradiated during the temperature rise corresponds to the carrier emission energy of the trap level that causes the thermoluminescence lost by it, and the behavior of the forbidden band level and the carrier capture and emission process In addition, a new measurement technique that comprehensively observes luminescence / non-light emission recombination processes was demonstrated.

  The specific operation of the above embodiment will be described.

  Although it depends on the energy band width of light emission / light reception and electronic materials, BGE photoexcitation is advantageous in the ultraviolet to visible photon energy region, and simple and quick measurement is possible, but in the infrared low energy region measurement. It's not so easy. On the other hand, although thermal excitation is effective for measurement in a low energy region, it takes time and is insufficient in accuracy and becomes difficult as energy increases. Thus, by organically combining photoexcitation and thermal excitation processes using AGE and BGE light, simple and highly accurate measurement can be realized in the entire energy region of the sample forbidden band energy width, and the above problems can be solved.

  Furthermore, the advantage of the two-wavelength excitation PL makes it possible for the first time to evaluate not only the trapping level but also other non-radiative recombination levels as a forbidden band level.

  In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.

  The method and apparatus for quantitatively measuring the level in the forbidden band by photoluminescence with thermal excitation according to the present invention clearly shows the origin of the level in the forbidden band, and through its removal, the material composition, fabrication process, device structure, etc. It is suitable for measuring tools for light emission, light reception and electronic materials and devices that can be easily optimized.

FIG. 3 is an energy band diagram of a semiconductor having two trap levels (energy E _T1 and E _T2 ) and one non-radiative recombination level (energy E _NT ) according to the present invention. FIG. 2 is an explanatory diagram showing a state in which electrons are captured only in the trap level 2 when the electrons are trapped in the trap levels 1 and 2 by AGE light and then heated to a temperature T ₂ in FIG. In addition to trapping electrons in all trap levels with AGE light, the method of the present invention allows only a single trap level (eg, trap level 2 with photon energy E _exc = E _T2 ) with a specific BGE light. It is explanatory drawing which shows the state which selectively captures an electron. It is a block diagram of the measuring device (system) in the forbidden band level by the photoluminescence which added the thermal excitation which shows the Example of this invention. It is a figure which shows the temperature dependence of the emitted light intensity at the time of adding BGE irradiation concerning this invention. It is a figure which shows the temperature dependence of the emitted light intensity when not applying BGE irradiation concerning this invention, and the energy of the capture level which brings about each peak.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AGE light source 2 BGE light source 3 Sample 4 Spectrometer 5 Photomultiplier tube 6 Digital oscilloscope 7 Boxcar integrator 8 Computer 9 Cooling and heating apparatus 10 Temperature control apparatus 11 Temperature sensor

Claims (2)

In the method for measuring the level in the forbidden band by photoluminescence (PL),
(A) Light emission / light reception and electronic material are irradiated with AGE light or BGE light of photon energy E _exc beforehand at a low temperature so that excited carriers (electrons or holes) are trapped in the trap level in the forbidden band,
(B) After blocking the AGE light or the BGE light, the photon energy at a certain intermediate temperature when observing the light emission by the carriers thermally released from the trap level as a function of temperature while increasing the temperature at a constant temperature rising rate. by irradiating BGE light E _B, and photoexcitation by BGE the trap level of the carriers then have to irradiate heat radiated by will will capture energy E _T <E _B, to produce a light emission at a time, this At a later temperature rise, no carriers are present at the trapping level of trapping energy E _T <E _B , so no light emission occurs, and the carrier reaches a temperature at which the carriers from the level of trapping energy E _T > E _B are thermally released. For the first time,
(C) From the reciprocal relationship between photoexcitation and thermal excitation, the energy of the forbidden band level is detected using specific photon energies E _exc and E _B , or a combination of different E _exc and E _B. A method for measuring a level in a forbidden band by photoluminescence with thermal excitation. In the measuring device of the level in the forbidden band by photoluminescence (PL),
(A) an AGE light source that emits AGE light;
(B) a BGE light source that emits BGE light;
(C) a cooling and heating device acting on the luminescent material as a sample;
(D) a temperature control device for controlling the temperature of the cooling and heating device;
(E) a sensor for detecting the temperature of the sample,
(F) Light emission, light reception, and electronic material are irradiated with AGE light or BGE light of photon energy E _exc in advance at a low temperature so that excited carriers (electrons or holes) are trapped in the trap level in the forbidden band. When the light emitted from the trapped level is observed as a function of temperature while the temperature is increased at a constant temperature increase rate by the sensor and the temperature control device after blocking light or BGE light, When BGE light of photon energy E _B is irradiated at a temperature, the carriers at the trap energy level E _T <E _B that would otherwise have been thermally radiated if not irradiated are photoexcited by BGE, causing light emission at once. , a Atsushi Nobori after this, <trapping level in the carrier does not occur are emission due to the absence, captured energy E _T of E _B> carrier of heat emission from the level of E _B capture energy E _T That allowed for the first time caused the following emission reached temperature, using a combination of a specific photon energy E _exc and E _B or a plurality of different E _exc and E _B, the reciprocal relationship between the excitation and thermal excitation, A device for measuring levels in a forbidden band by photoluminescence with thermal excitation, characterized by measuring the energy of the level in the forbidden band.

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