JP2005072368A - Semiconductor light emitting delement, semiconductor laser element, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting element superior to a color purity by decreasing a shift amount of a light emitting peak wavelength varied by a driving current entered to a light emitting layer and an image display device capable of displaying a superior image with a simple driving circuit by constructing an image displaying part with the semiconductor light emitting element. <P>SOLUTION: The shift amount of the light emitting peak wavelength to the driving current can be decreased by making a layer thickness of an InGaN layer 16 of a light emitting layer one atomic layer to eight atomic layer. Further, the image displaying device having the image displaying part having those semiconductor light emitting elements arranged can emit the light of an approximately constant light emitting peak wavelength even when the driving current is varied. Adjusting an In composition ratio of the InGaN layer of the light emitting layer can emit a blue or a green light and can decrease the shift amount of the light emitting peak wavelength. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor light emitting device in which the emission peak wavelength and half width of light generated in a light emitting layer hardly change depending on the current injected into the light emitting layer. Furthermore, the present invention relates to an image display device that can have a simple configuration of a drive circuit that performs gradation of a display image. The present invention also relates to a semiconductor laser element that can generate light having a wavelength that has been difficult to cause laser oscillation by suppressing an increase in threshold current during laser oscillation.

  A semiconductor light-emitting element formed using a gallium nitride compound semiconductor (hereinafter referred to as a GaN-based semiconductor) as a main material can emit light having a wide wavelength range from blue to orange. It attracts attention as a semiconductor light emitting device capable of emitting light of a short wavelength. In addition, an image display device in which a light emitting diode (LED), which is an example of such a semiconductor light emitting element, is arranged to form an image display unit has been developed.

  Such a semiconductor light-emitting element is formed by stacking an n-type conductive semiconductor layer, a light-emitting layer, and a p-type conductive semiconductor layer on a substrate. For example, an InGaN layer is used as a light-emitting layer. When formed, the emission wavelength can be adjusted by adjusting the composition ratio of indium (In). Further, the present invention is not limited to a single quantum well structure having a single light emitting layer, and a multiple quantum well structure in which a barrier layer is formed between a plurality of light emitting layers may be formed.

  Usually, a semiconductor light-emitting device mainly composed of a GaN-based semiconductor has a double heterostructure in which the light-emitting layer is sandwiched between different types of semiconductor layers having different compositions, and a piezo electric field or misfit dislocation caused by lattice mismatch occurs. There are many cases. Piezoelectric fields and misfit dislocations generated inside the element cause a reduction in the light emission efficiency of the semiconductor light emitting element.

  Specifically, when the InGaN layer, which is the light emitting layer, is thickened, there is a tendency for the light emitting efficiency to decrease due to the introduction of crystal defects, or the light emitting efficiency to decrease due to the piezoelectric field, and when the InGaN layer is made thin, light is emitted. Since carriers pass through the layer, the carrier injection efficiency tends to decrease and the light emission efficiency tends to decrease. Therefore, the light emitting layer having a thickness of about 3 nm as described above is adopted in consideration of tradeoffs of causes for reducing the light emission efficiency such as introduction of crystal defects, generation of a piezoelectric field, and a decrease in carrier injection density. There are many cases.

Further, various techniques for increasing the light emission efficiency of the semiconductor light emitting device using the above-described InGaN layer as a light emitting layer have been proposed. In particular, the thickness of the light emitting layer is described in detail in Patent Document 1.
Japanese Patent Laid-Open No. 10-229217

  However, even when the light emitting layer having a thickness of about 3 nm is formed, there is a problem that the piezo electric field exists and the light emission wavelength is changed by changing the current injected into the semiconductor light emitting element. In particular, when the semiconductor light-emitting element described above is used as a light source of an image display device, it is important to suppress a change in emission wavelength by reducing a variation in injection current injected into the light-emitting element.

  According to Patent Document 1 described above, there is disclosed a result of comparing the shift amount of the emission peak wavelength by changing the injection current when the emission peak wavelength is 485 nm, 550 nm, and 570 nm. No mention is made of the shift amount of the emission wavelength peak included in the wavelength range of light suitable as a blue or green light source of the image display device. Further, according to Patent Document 1, no detailed study has been made on the range of 440 to 480 nm, which is a light wavelength suitable as a blue light source, or 500 to 550 nm, which is a light wavelength suitable as a green light source. .

  Therefore, the emission peak due to the change in emission efficiency, emission peak wavelength distribution width, and injection current in the range of the wavelength of light required for the semiconductor light emitting element constituting the image display unit of the image display device such as a multi-color display. The amount of wavelength shift has not been studied in detail, and the semiconductor light emitting device having an element structure suitable as a blue or green light source of an image display device has not yet obtained sufficient performance.

  Furthermore, when an image display device such as a multi-color display is driven to display an image, pulse width modulation (PWM) according to the gradation of the image display unit is performed on the image signal. Then, the current subjected to the pulse width modulation is injected into the semiconductor light emitting element to perform gradation of the image display unit. Normally, such pulse width modulation is performed by a high-frequency circuit provided in the image display device, so that the drive circuit of the image display device has a complicated configuration, and further processing of the image signal when driving the image display device is performed. It was complicated. Therefore, there has been a demand for a technique that allows a drive circuit provided in an image display apparatus to have a simple configuration and that can easily process an image signal. Furthermore, there is a need for a semiconductor light-emitting element that can widen the color reproduction range of an image display device by suppressing a decrease in color purity. In such a semiconductor light-emitting element, the current injected into the semiconductor light-emitting element changes. In this case, it is desirable that the emission peak wavelength hardly shifts and that the full width at half maximum of the semiconductor light emitting element is reduced.

  In addition, the present invention is not limited to the semiconductor light-emitting device mounted on the image display device described above, and in a semiconductor laser device composed mainly of a GaN-based semiconductor, a threshold current at the time of laser oscillation due to the influence of the piezoelectric field inside the device. There is also a problem that increases. In particular, it has been observed that the threshold current increases extremely in the wavelength range of light exceeding 450 nm, and only lasers with oscillation wavelengths up to 480 nm have been realized.

  Therefore, the present invention has been made in view of the above-described circumstances, and has a device structure in which the shift amount of the emission peak wavelength due to the change of the injection current is suppressed, and is suitable as a light source for an image display device. It is an object of the present invention to provide a light emitting element, an image display device equipped with the light emitting element, and a semiconductor laser element in which a threshold current when a long wavelength laser beam is oscillated is reduced.

  A semiconductor light-emitting device according to the present invention is a semiconductor light-emitting device that constitutes an image display unit of an image display device, and is a light-emitting layer mainly composed of a gallium nitride-based compound semiconductor and having a layer thickness of 1 atomic layer to 8 atomic layers. And the gradation of the image display unit is controlled by adjusting the amplitude of the current injected into the light emitting layer. According to the semiconductor light emitting device of the present invention, the emission peak wavelength hardly shifts due to the change in the amplitude of the current injected into the light emitting layer, and therefore the gradation of the image display unit can be controlled by the amplitude of the current. . Such a semiconductor light emitting device is excellent in color purity and suitable for performing high quality image display. Further, in an image display device having an image display unit in which such semiconductor light emitting elements are arranged, frequency conversion of injected current performed for the purpose of displaying a finer image can be reduced and the semiconductor light emitting elements are driven. The driving circuit to be configured can have a simple configuration. In addition, by including data indicating gradation in the frequency and amplitude of the injection current, it is possible to perform finer gradation as compared with the case where gradation is performed only by frequency conversion of the injection current.

  Furthermore, in the semiconductor light emitting device according to the present invention, the light emitting layer is a gallium nitride compound semiconductor layer containing indium, and the wavelength of light generated in the light emitting layer is included in a wavelength range of blue or green light. You may do it. In particular, the wavelength of light generated in the light emitting layer can be included in a wavelength range of 440 to 480 nm or 500 to 550 nm, and the semiconductor light emitting device according to the present invention has excellent color purity. It can also be used as a blue or green light source. Further, when such a semiconductor light emitting element is used as a blue or green light source, the indium composition ratio in the light emitting layer may be set to 15 to 40%.

  In the semiconductor light emitting device according to the present invention, a semiconductor layer having p-type or n-type conductivity is formed on one side of the light-emitting layer, and the light-emitting layer and the p-type or n-type conductive layer are formed. A buffer layer having a band gap larger than the band gap of the light emitting layer and smaller than the band gap of the p-type or n-type conductive semiconductor layer is formed between the first semiconductor layer and the second semiconductor layer; Also good. According to such a buffer layer, it is possible to prevent carriers from recombining with the light emitting layer when the light emitting layer is thinned. Thereby, it becomes possible to reduce that a carrier passes a light emitting layer, without light emission by recombination, and can improve luminous efficiency.

  The semiconductor laser device according to the present invention is a multilayer comprising a light emitting layer having a layer thickness of 1 to 8 atomic layers and a crystal layer formed on the light emitting layer, the main material being a gallium nitride compound semiconductor. And an end face formed by cleaving the body. According to the semiconductor laser device of the present invention, since the layer thickness of the light emitting layer is 1 atomic layer to 8 atomic layer, the threshold current at the time of laser oscillation can be reduced. Further, by setting the In composition ratio of the light emitting layer to a predetermined value, it becomes possible to oscillate a laser in a wavelength range that has been conventionally difficult.

  An image display device according to the present invention includes a gallium nitride compound semiconductor as a main material, and an image display unit formed by disposing a semiconductor light emitting element having a light emitting layer having a layer thickness of 1 to 8 atomic layers, Gradation control means for controlling the gradation of the image display unit by adjusting the amplitude of the current injected into the light emitting layer. According to the image display device of the present invention, since the frequency conversion of the current for driving the semiconductor light emitting element can be reduced, the drive circuit for driving the semiconductor light emitting element can be simply configured. Furthermore, since the information about the gradation of the image can be included in the current amplitude, it is possible to perform not only the gradation using the current frequency but also a finer gradation using the current amplitude. .

  According to the semiconductor light emitting device according to the present invention, light having a substantially constant emission peak wavelength can be generated even when the driving current is changed, and the half width of the emission peak wavelength is small, so that the color purity is excellent. Can generate light. According to an image display apparatus having an image display unit in which such a semiconductor light emitting element is arranged, not only the frequency of the drive current of the semiconductor light emitting element but also the amplitude of the display image can be controlled by controlling the amplitude. Can be controlled. As a result, the load on the circuit that converts the frequency of the drive current can be reduced, and image display can be performed with a simple circuit. Furthermore, since gradation can be performed using both the frequency and amplitude of the drive current, finer gradation can be performed.

  Hereinafter, a semiconductor light emitting device, an image display device having the semiconductor light emitting device and a semiconductor laser device according to the present invention will be described in detail with reference to the drawings.

  The semiconductor light emitting device according to the present invention is formed using a GaN-based compound semiconductor as a main material, and a single quantum in which a p-type semiconductor layer and an n-type semiconductor as current injection layers are formed on both sides of the light emitting layer, respectively. It has a well structure or a multiple quantum well structure in which a barrier layer is formed between a plurality of light emitting layers.

  Furthermore, the light emitting layer formed in the semiconductor light emitting device according to the present invention has a layer thickness of 1 atomic layer to 8 atomic layer, and according to the light emitting layer having such a layer thickness, a change in injection current is achieved. The shift width of the emission peak wavelength with respect to can be reduced to a sufficient size. As a result, the semiconductor light emitting device according to the present invention has a light emission peak wavelength shift smaller with respect to a change in current injected into the device, and is a light emitting device suitable for an image display device.

  For example, the semiconductor light emitting device according to the present invention is a light emitting device capable of emitting light at a wide angle such as a light emitting diode suitable for an image display device, and particularly as a light source of an image display device such as a multi-color display. It is a light-emitting element that emits blue or green light.

  The semiconductor light emitting device according to the present embodiment is a semiconductor light emitting device formed by a metal organic compound vapor phase epitaxy (MOCVD (MOVPE) method). For example, the main component of a sapphire substrate introduced into a metal organic vapor phase epitaxy apparatus. It is a light emitting device formed by growing a required crystal layer on a surface.

  The semiconductor light emitting device according to the present embodiment will be described in detail with reference to FIGS. 1 and 2. The main surface of the sapphire substrate for performing element formation is a C surface that is usually used for growing a GaN-based semiconductor layer, and by supplying trimethylgallium and ammonia at 500 ° C. using hydrogen gas as a carrier gas. The GaN layer 2 having a layer thickness of 30 nm is formed on the main surface of the sapphire substrate. The GaN layer 2 serves as an underlying growth layer for the crystal layer on which the crystal is grown, reduces the dislocation density caused by lattice mismatch when forming the crystal layer constituting the device body, and produces a high-quality crystal layer. It can be grown on the GaN layer 2. The substrate on which the elements are formed is not limited to a sapphire substrate, and a GaN substrate can also be used.

  Subsequently, the supply of trimethylgallium is temporarily stopped, the temperature in the apparatus is raised to 1050 ° C., the supply of trimethylgallium is started again, and silicon is doped while supplying silane as a silicon (Si) source. The GaN layer 3 is grown to a layer thickness of 2 μm.

  Further, an n-type cladding layer 4 and an n-type guide layer 5 doped with Si are sequentially formed on the n-type GaN layer 3. The n-type cladding layer 4 is a crystal layer made of an AlGaN / GaN superlattice, and the n-type guide layer 5 is an InGaN layer.

  Subsequently, the supply of silane and trimethylgallium is stopped, the carrier gas is switched to nitrogen gas, the temperature in the apparatus is lowered, and in a state where the temperature is stable, trimethylindium and gallium (Ga) sources that are indium (In) sources are used. A certain trimethylgallium is supplied to form the multiple quantum well layer 6. The multiple quantum well layer 6 is formed by sequentially laminating an InGaN layer 15, an InGaN layer 16, and a barrier layer 17. In this embodiment, the multiple quantum well layer 6 includes the InGaN layer 15, the InGaN layer 16, and the barrier. The layer 17 has a structure in which five periods are formed. The semiconductor light emitting device 1 according to this embodiment has a multiple quantum well structure composed of a single quantum well structure of five periods, but the number of single quantum well layers constituting the multiple quantum well layer 6 is the same as that of this embodiment. The number of layers in the form is not limited, and one single quantum well structure may be formed.

  The InGaN layer 15 is formed between the n-type GaN layer 3 and the first InGaN layer 16, and has a larger band gap than the InGaN layer 16 that is a light emitting layer and a smaller band gap than the n-type guide layer 5. Is a layer. The InGaN layer 15 is a buffer layer for efficiently confining carriers injected into the InGaN layer 16 that is a light emitting layer. Further, the band gap of the InGaN layer 15 formed between the p-type guide layer 7 and the fifth InGaN layer 16 is larger than the band gap of the InGaN layer 16 that is the light emitting layer, and each InGaN layer 15. Smaller than the band gap of the n-type guide layer 5 and the p-type guide layer 7 described later. The layer thickness of the InGaN layer 15 is preferably about 1 to 20 nm, for example, and this makes it possible to efficiently confine carriers supplied to the InGaN layer 16 that is the light emitting layer, thereby increasing the light emission efficiency. Is possible.

  The thickness of the InGaN layer 16 that is the light emitting layer is 1 atomic layer to 8 atomic layer. According to the light emitting layer having such a layer thickness, the shift of the emission wavelength peak is caused by the injection current injected into the light emitting layer. Almost never occurs due to fluctuations. By setting the composition ratio of In contained in the InGaN layer 16 which is a light emitting layer to a predetermined value, blue light whose emission peak wavelength is 440 nm to 480 nm, or green light whose emission peak wavelength is 500 nm to 550 nm Can be emitted from the light emitting layer, and the semiconductor light emitting element can be a light emitting element suitable for an image display device such as a multi-color display. For example, in order to emit blue or green light, the composition ratio of In contained in the InGaN layer 4 that is a light emitting layer may be set in a range of 15 to 40%. If the composition ratio is 17 to 20%, blue light can be emitted, and if the In composition ratio is 20 to 30%, green light can be emitted.

  Subsequently, after forming the p-type guide layer 7 on the upper side of the multiple quantum well layer 6, the carrier gas is switched to hydrogen, cyclopentadienylmagnesium as a magnesium (Mg) source, and trimethylgallium as a gallium (Ga) source. Then, the Mg-doped p-type cladding layer 8 and the p-type GaN layer 9 are grown. Further, after the element body made of these semiconductor layers is taken out from the metal organic vapor phase epitaxy apparatus, the p-type GaN layer 9 is activated by annealing for 10 minutes in a nitrogen atmosphere at 800 ° C.

  Subsequently, the crystal layer as the element body is etched from above by a reactive ion etching (IRE) apparatus so that the n-type GaN layer is exposed, and a titanium thin film and an aluminum thin film are formed on the surface where the n-type GaN layer 3 is exposed. An n-electrode 11 made of a laminated Ti / Al multilayer film is formed. Further, a Ni / Pt / Au multilayer film made of a Ni thin film, a platinum thin film and a gold thin film is formed on the upper surface of the p-type GaN layer 9 to form the p electrode 10, thereby completing the semiconductor light emitting device 1. Such a semiconductor light emitting element 1 is, for example, a light emitting diode having a large spread in the light emitting direction, and is suitable for an image display device.

  The semiconductor light emitting element 1 may be a resin chip coated with a resin, and the semiconductor light emitting element 1 may be covered with a resin by a transfer process when the semiconductor light emitting element 1 is formed. According to such a resin chip, handling when the semiconductor light emitting element is arranged in the image display device can be easily performed.

  Next, the configuration of the image display device equipped with the semiconductor light emitting element according to the present embodiment will be described in detail. FIG. 3 is a block diagram showing a configuration of a multi-color display equipped with the semiconductor light emitting device according to the present embodiment.

  As shown in FIG. 3, the multi-color display includes an image display unit 31 in which light emitting diodes are arranged, and a drive unit 32 that supplies a drive current to the image display unit in accordance with an image signal.

  The image display unit 31 includes a light emitting diode that constitutes a pixel and emits red, green, and blue light, respectively, and the red, green, and blue light emitting diodes constitute one pixel as a set. Among such light emitting diodes, the thickness of the light emitting layer of a light emitting diode that is a blue or green light source is 1 to 8 atomic layers, and the light emitting diode that is a blue light source has an In composition ratio. The In composition ratio of the light emitting diode which is 17% to 20% and is a green light source is 20 to 30%. The element structure of the light emitting diode that is used as such a blue or green light source is substantially the same as that of the semiconductor light emitting element 1 described above.

  The drive unit 32 includes an AD converter 21, a memory 22, a luminance conversion unit 23, a γ correction unit 24, a synchronization separation unit 25, a PLL (Phase Locked Loop) 26, a synchronization clock unit 27, a control unit 30, and a column driver. 28 and a row driver 29.

  The AD converter 21 converts an analog signal such as an image signal into a digital signal. The image signal includes RGB signals (R: red, G: green, B: blue), and the memory 22 stores the digitally converted image signal, and the image signal is sent to the luminance separation unit 23 while synchronizing with the PLL 26. send. The luminance separation unit 23 separates the luminance signal from the image signal, sends the luminance signal to the control unit 30, and sends the image signal to the γ correction unit 24. The γ correction unit 24 is a general-purpose γ correction circuit, and sends, for example, an image signal obtained by correcting γ = 2.2 to an input signal to the column driver 28.

  The column driver 28 includes a pulse width modulation circuit and a current source. The pulse width modulation circuit controls the frequency of the drive current for driving the light emitting diodes arranged in the image display portion 31, and the control unit 30 sets the amplitude of the drive current supplied from the current source of the column driver 28. Control. The drive current has a pulse waveform, and at least one of frequency and amplitude is controlled in accordance with the gradation. In this manner, the light emitting diode is driven by the driving current in which at least one of the frequency and the amplitude is controlled, and image display is performed. That is, as compared with the conventional case where gradation is controlled only by pulse width modulation using a high frequency circuit, the level of the image display unit 31 is determined by the amplitude of the drive current supplied to the light emitting diodes arranged in the image display unit 31. Key can be controlled. Thereby, not only the frequency conversion of the image signal necessary for expressing the gradation can be reduced, but also a finer gradation can be performed.

For example, when the number of pixels formed in the image display unit 31 is 640 × 480 = 307200 pixels, the scanning frequency fs is 28.8 kHz (60 Hz × 480 lines) when the gradation is 8 bits. Conventionally, it is necessary to generate a pulse signal corresponding to the number of bits in one scan period, PWN frequency was necessary only 7.37MHz is 256 times the scanning frequency fs ^{(2 8-fold).} According to the light emitting diodes arranged in the image display device according to the present embodiment, since the shift of the emission wavelength peak tends to be small with respect to the change of the drive current, the gradation of the display image is performed by the amplitude of the drive current be able to.

  Further, the sync separator 25 receives the horizontal sync signal and the vertical sync signal and sends them to the PLL 26. The PLL 26 sends a signal to the synchronous clock unit 27, the synchronous clock unit 27 sends a clock signal for controlling the column driver 28 to the control unit 30, and the control unit 30 adjusts the amplitude of the drive current in accordance with this clock signal. Control. The synchronous clock unit 27 synchronizes the column driver 28 and the row driver 29.

  Thus, the drive unit 32 can include a part or all of the information on the number of bits representing the gradation of the image displayed on the image display unit in the amplitude of the drive current for driving the light emitting diode. . As a result, part or all of the PWM frequency can be included in the amplitude of the drive current, and the load on the frequency conversion circuit such as a high-frequency circuit can be reduced. Further, when the gradation of the display image is performed only by controlling the amplitude of the drive current, the gradation of the display image can be performed without providing a high-frequency circuit in the image display device. Furthermore, since the shift amount of the light emission peak wavelength of the light emitting diode is small due to the change in the amplitude of the drive current, it is possible to control the gradation with a small change in the hue. That is, according to the image display apparatus according to the present embodiment, it is possible to reduce the load on the drive unit 32 and perform high-quality image display in which the change in hue is suppressed.

Next, examples performed by the inventors of the present application will be described. Note that the semiconductor light-emitting elements used in the examples have substantially the same element structure as the semiconductor light-emitting elements described above, and thus common portions are denoted by the same reference numerals.
Example

  With reference to Table 1 and FIGS. 4 to 6, experimental results conducted by the inventors of the present invention using a semiconductor light emitting device having an element structure substantially similar to the semiconductor light emitting device described above will be described. In this experiment, the semiconductor light emitting device was evaluated for the shift of the emission wavelength peak with respect to the excitation intensity, the half width, and the change of the emission intensity.

  Table 1 shows the configuration of Sample B used in this experiment in detail. In Table 1, among the crystal layers constituting the multiple quantum well layer 6, the InGaN layers 15 and 16, the barrier layer 17 formed above the n-type guide layer 5, and the lower side of the p-type guide layer 7. Only the InGaN layers 15 and 16 formed in FIG. 6 are shown, and the second to fourth single quantum well layers counted from the n-type guide layer 5 side among the single quantum well layers constituting the multiple quantum well layer 6 are shown. Although the detailed structure is omitted, the second to fourth single quantum well layers are substantially the same as the first and fifth single quantum well layers counted from the n-type guide layer 5. It has a configuration.

なお、本実験で用いた試料Ａ，Ｂは半導体発光素子１と略同様の構成を有していることから共通する部分については同一の参照符号を用いて説明する。本実験においては、発光層であるＩｎＧａＮ層１６の層厚及びＩｎ組成比を変えた場合の励起強度に対する発光波長ピークのシフト、半値幅及び発光強度の変化を比較した。試料ＡはＩｎＧａＮ層の層厚が２．５ｎｍであり、Ｉｎ組成比は１７％である。また、他方の試料Ｂは、ＩｎＧａＮ層の層厚が１．８ｎｍであり、Ｉｎ組成比は１９％である。

Since the samples A and B used in this experiment have substantially the same configuration as the semiconductor light emitting element 1, common portions will be described using the same reference numerals. In this experiment, the shift of the emission wavelength peak, the half-value width, and the change of the emission intensity with respect to the excitation intensity when the thickness and the In composition ratio of the InGaN layer 16 as the emission layer were changed were compared. Sample A has an InGaN layer thickness of 2.5 nm and an In composition ratio of 17%. The other sample B has an InGaN layer thickness of 1.8 nm and an In composition ratio of 19%.

  FIG. 4 is a graph showing the shift amount of the emission wavelength peak of samples A and B with respect to the excitation intensity. As shown in FIG. 4, the emission wavelength peak of sample A tends to have a larger change with respect to the excitation intensity than the emission wavelength peak of sample B. Specifically, sample B changes its emission wavelength peak by about 450 to 448.5 nm as the excitation intensity changes from 0.1 to 1.0, but sample A emits light in the same excitation intensity range. The peak wavelength changes to about 452-440 nm. That is, in the range of excitation intensity from 0.1 to 1.0, the emission peak wavelength of sample A shifts by about 12 nm, whereas the shift amount of the emission peak wavelength of sample B is as slight as about 1.5 nm. It's just a change. The tendency of the shift amount of the emission peak wavelength with respect to the excitation intensity shows the same tendency when the injection current to the semiconductor light emitting element fluctuates, and thus has a layer thickness of 1 to 8 atomic layers. It has been found that the semiconductor light emitting device in which the light emitting layer is formed tends to reduce the shift of the emission peak wavelength.

  From this experiment, it is considered that the thickness of the light emitting layer is more preferably 1.8 nm or less. Furthermore, the semiconductor light emitting element used for the blue or green light source of the multicolor display may have an In composition ratio in the range of 17 to 20% in order to emit blue light. In order to emit green light, the In composition ratio of the light emitting layer may be set to 20 to 30%.

  FIG. 5 is a graph showing changes in the half-value width of the emission peak wavelength with respect to the excitation intensity when the samples A and B emit light. As shown in FIG. 5, it was found that the full width at half maximum of sample B was smaller than the full width at half maximum of sample A at all excitation intensities evaluated in this experiment, and the emission peak wavelength spread was small. Further, the change in the half-value width with respect to the excitation intensity is smaller in the sample B than in the sample A. Specifically, the half-value width of the sample A changes by about 5 nm in the range of the excitation intensity of 0.1 to 1.0. The change in the half width of Sample B was about 2 nm. Thus, the change in the hue of the semiconductor light emitting element can be reduced by reducing the half width of the emission wavelength. An image display apparatus including an image display unit in which such semiconductor light emitting elements are arranged has excellent image quality.

  Further, FIG. 6 is a graph showing the emission intensity with respect to the excitation intensity of samples A and B. As shown in FIG. 6, both the samples A and B tend to increase in emission intensity as the excitation intensity is increased. However, in the range of strong excitation in which the excitation intensity exceeds about 0.3, the emission of the sample A The emission intensity of sample B tended to be higher than the intensity. Thus, according to this experiment, it was also confirmed that the emission intensity can be increased by reducing the thickness of the InGaN layer 16 serving as the light emitting layer. In addition, although the layer thickness of the light emitting layer of sample B is 1.8 nm (about 7 atomic layers), if the layer thickness of the light emitting layer is 1 atomic layer to 8 atomic layers, the light emitting efficiency of the semiconductor light emitting element is the layer thickness. This can be increased compared to a thicker light emitting layer.

  In this example, the experiment was performed in the range where the emission wavelength was blue. However, in the range of the green wavelength that is longer than blue, the influence of the piezoelectric field is usually large. Therefore, it is more preferable to make the thickness of the light emitting layer thinner than when emitting blue light. For example, when the emission peak wavelength is 520 nm, the thickness of the light emitting layer is preferably 1.5 nm or less.

  According to this example, in the semiconductor light emitting device having a light emitting layer thickness of 1 atomic layer to 8 atomic layer, the shift amount of the emission wavelength peak due to the change in excitation intensity is further reduced, and the layer thickness of 9 atomic layers or more. Compared with a semiconductor light emitting element having a high color purity of emitted light. In particular, when used as a light source for an image display unit of a multi-color display, the image display device can display superior image quality as compared with a case where a conventional semiconductor light emitting element such as a light emitting diode is used.

  Further, in the semiconductor light emitting device in which the thickness of the light emitting layer exceeds 8 atomic layers, the color purity is low, and the color of light is changed by the change of the drive current for causing the semiconductor light emitting device to emit light, whereas the sample B According to the semiconductor light emitting device as described above, it is possible to increase the color purity and the color reproduction range, and it is also possible to reduce a change in hue due to a change in driving current.

  In addition, when the wavelength of light generated in the semiconductor light emitting element greatly changes due to a change in current value as in the conventional case, the amplitude of the drive current is fixed and the drive is performed to express the gradation of the displayed image. A high-frequency circuit for performing the pulse width modulation of the current is necessary, and there is a limit to the minimum pulse width after the drive current is modulated. However, according to the semiconductor light emitting device such as Sample B evaluated in this experiment, a part or all of the gradation of the display image can be expressed by modulating the amplitude of the drive current, and the frequency such as pulse width modulation can be expressed. Conversion can be reduced. In particular, a semiconductor light-emitting element that emits light having a wavelength of 440 to 480 nm or 500 to 550 nm can be used as a blue or green light source of an image display device, respectively, and improves the image quality of the image display device. It is suitable for this purpose.

  Further, the InGaN layer 15 was formed so as to have an element structure substantially the same as that of the sample B, set the In composition ratio of the InGaN layer 15 as a buffer layer to 7%, and further to have a layer thickness of 20 nm or less. Such a semiconductor light emitting device has improved light emission efficiency as compared with the case where a buffer layer such as the InGaN layer 15 is not formed. In general, a semiconductor light emitting device in which a thin light emitting layer is formed passes through a well layer without light emission due to sufficient recombination of carriers in the InGaN layer 16 which is a light emitting layer at the time of current injection, but is a light emitting layer. By making the energy level on the n-side of the InGaN layer 16 larger than that of the outer semiconductor layer and smaller than that of the outer semiconductor layer, carriers can be effectively confined in the vicinity of the light emitting layer without causing light emission. Carriers passing through the light emitting layer can be reduced. Thereby, luminous efficiency can be improved. Further, such a buffer layer may be formed on the p side of the light emitting layer, and further, a buffer layer may be formed on both sides of the light emitting layer.

  Furthermore, according to the semiconductor laser element having the element structure substantially the same as that of the sample B, the threshold current at the time of laser oscillation can be reduced. For example, when forming an end face of a semiconductor light emitting element such as sample B, the crystal layer constituting the semiconductor light emitting element is cleaved, and this end face is used as an optical resonant surface, thereby making the semiconductor light emitting element a semiconductor laser element. be able to. Also in such a semiconductor laser device, since the layer thickness of the light emitting layer is from 1 atomic layer to 8 atomic layer, the emission half-value width of spontaneous emission light is narrow, and the change in the emission wavelength accompanying the increase in carrier density is also small. By taking advantage of such advantages, laser oscillation can be performed with a lower threshold current than in the past. Further, it is possible to generate laser light having a wavelength in a wavelength region larger than 480 nm by adjusting the In composition ratio in the light emitting layer.

It is sectional drawing which shows the structure of the semiconductor light-emitting device concerning this embodiment. It is principal part sectional drawing which shows the structure of the multiple quantum well layer of the semiconductor light-emitting device in detail. It is a block diagram which shows the structure of the image display apparatus concerning this embodiment. It is a figure which shows the experimental result in an Example, and is the graph which compared the change of the light emission wavelength peak with respect to excitation intensity | strength. It is a figure which shows the experimental result in an Example, and is the graph which compared the half value width with respect to excitation intensity | strength. It is a figure which shows the experimental result in an Example, and is the graph which compared the emitted light intensity with respect to excitation intensity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor light-emitting device 6 Multiple quantum well layer 17 Barrier layer 22 Memory 23 Luminance separation part 25 Synchronization separation part 27 Synchronization clock part 28 Column driver 29 Low driver 30 Control part 31 Image display part 32 Drive part

Claims (10)

A semiconductor light emitting element constituting an image display unit of an image display device,
The main material is a gallium nitride compound semiconductor, and the light emitting layer has a thickness of 1 to 8 atomic layers,
The gradation of the image display unit is controlled by adjusting the amplitude of the current injected into the light emitting layer. The light emitting layer is a gallium nitride compound semiconductor layer containing indium,
2. The semiconductor light emitting element according to claim 1, wherein a wavelength of light generated in the light emitting layer is included in a wavelength range of blue or green light. 3. The semiconductor light emitting element according to claim 2, wherein the wavelength of light generated in the light emitting layer is included in a wavelength range of 440 to 480 nm or 500 to 550 nm. 3. The semiconductor light emitting device according to claim 2, wherein a composition ratio of indium in the light emitting layer is 15 to 40%. A semiconductor layer having p-type or n-type conductivity is formed on one side of the light emitting layer,
Between the light emitting layer and the semiconductor layer having the p-type or n-type conductivity, a semiconductor having a band gap larger than that of the light-emitting layer and having the p-type or n-type conductivity. The semiconductor light emitting element according to claim 1, wherein a buffer layer having a band gap smaller than that of the layer is formed. The semiconductor light emitting element according to claim 5, wherein the buffer layer has a thickness of 1 nm to 20 nm or less. A plurality of the light emitting layers;
The semiconductor light emitting device according to claim 1, comprising a multiple quantum well structure in which a barrier layer is formed between one light emitting layer and another light emitting layer. A luminescent layer having a gallium nitride compound semiconductor as a main material and a layer thickness of 1 to 8 atomic layers;
A semiconductor laser device comprising: an end face formed by cleaving a stacked body including a crystal layer formed to overlap the light emitting layer. An image display unit formed by disposing a semiconductor light-emitting element having a light-emitting layer whose main layer is a gallium nitride compound semiconductor and having a layer thickness of 1 to 8 atomic layers;
An image display apparatus comprising: gradation control means for controlling the gradation of the image display unit by adjusting an amplitude of current injected into the light emitting layer. The image display device according to claim 9, wherein the waveform of the current injected into the light emitting layer is a pulse wave.

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