KR20070078935A - Projection system employing the semiconductor diode - Google Patents

Abstract

A projection system using a semiconductor diode is provided to improve light efficiency and achieve high light modulation speed by allowing a semiconductor diode to transmit or absorb light according a wavelength of the light. A light source(110) emits white light. A color filter(115) separate the white light into a plurality of different single-color rays in a time sequence. A light modulator(120) modulates the separate single-color rays according to each color signal, and includes a semiconductor diode arranged for each pixel. The semiconductor diode is composed of a p-type semiconductor layer, an intrinsic semiconductor layer, and an n-type semiconductor layer, and absorbs or transmits the separated single-color ray according to a magnitude of a reverse bias voltage. A projection lens projects an image obtained by modulation of the light modulator toward a screen.

Description

Projection system employing the semiconductor diode

1 is a view showing the configuration of a projection system using a transmissive LCD according to the prior art.

2 is a view showing the configuration of a DLP (Digital Light Processing) projection system using a DMD panel according to the prior art.

3 is a diagram showing the configuration of a projection system according to an embodiment of the present invention.

4 is an enlarged view of a portion A of the optical modulator shown in FIG. 3.

5 is a cross-sectional view taken along the line VV ′ of FIG. 4.

6 is a graph schematically illustrating a change in absorption spectrum according to a reverse bias voltage.

7 is a graph measuring the change in absorption spectrum according to the reverse bias voltage.

<Explanation of symbols for the main parts of the drawings>

110 .... light source 115 .... color filter

117 .... Glass Road 120 .... Light Modulator

125 .... Projection Lens 140 .... Semiconductor Diode

141 .... N-type electrode 143 .... P-type electrode

145 P-type semiconductor layer 147..Intrinsic semiconductor layer

149 ... N-type semiconductor layer 151 ... transparent electrode

PL _m .... P-terminal line NL _k .... N-terminal line

The present invention relates to a projection system, and more particularly, to a projection system having a structure having a high light efficiency and a fast light modulation rate.

In recent years, display devices have become light and thin, as well as large screens, and as such a display, a projector or a projection TV has become one solution that can achieve a large screen.

Micro display devices that are emerging as new technologies for such projection systems include transmissive liquid crystal display (LCD) panels, reflective liquid crystal on silicon (LCoS) panels, and digital micromirror device (DMD) panels. It is classified into 1 panel type, 2 panel type, and 3 panel type according to the usage of dogs.

In the case of a transmissive LCD, a three panel method is generally used. In the case of LCoS, a three panel method, a two panel method, and a one panel method are generally used. In the case of a DMD, a one panel method is generally used.

1 is a view showing the configuration of a projection system using a transmissive LCD according to the prior art. Referring to the drawings, a projection system using a transmissive LCD includes a light source 10 and first and second dichroic mirrors 15a and 15b that separate light emitted from the light source 10 into red, green, and blue colors. First, second, and third LCD panels 20a, 20b, and 20c for modulating light separated from the dichroic lenses 15a and 15b according to an input signal, and the first, second, and third devices. And a color synthesizing prism 25 which synthesizes images from the LCD panels 20a, 20b, and 20c. Reference numeral 18 denotes a mirror.

Such a projection system has a problem in that the light efficiency is low due to the large light absorption of the polarizer, which is a component of the LCD panel 20, while having a bulky structure by adopting a three-panel method. In addition, since the LCD panel modulates light by the arrangement of liquid crystals between alignment layers, a liquid crystal whose alignment direction is changed according to a control signal takes a long time to return to the alignment direction.

2 is a diagram showing the configuration of a one-panel digital light processing (DLP) projection system using a DMD panel according to the prior art. Referring to the drawings, the DLP projection system includes a light source 30, a color filter 35 for sequentially dividing red, green, and blue light with time, and a DMD element for sequentially displaying screen information of each color. 40) and a projection lens 45 for projecting light from the DMD element 40 onto the screen.

As such, the projection system employing the DMD element has the advantage of reducing the number of optical parts by adopting the one-panel method due to the higher light efficiency than using the LCD panel. There is a problem that must be done. In addition, a phenomenon of light splashing occurs at the edge portion of the micromirror employed in the DMD element, which may result in a halo effect in which gray bands are generated around the image.

Accordingly, an object of the present invention is to provide a projection system having a high light efficiency and a high light modulation speed while minimizing the number of optical components by adopting a one panel method.

Projection system according to the present invention for achieving the above object, a light source for illuminating white light; and a color filter for separating the white light into a plurality of different monochromatic light in sequential time; and the separated monochromatic light according to each color signal An optical modulator comprising a P-type semiconductor layer, an intrinsic semiconductor layer, and an N-type semiconductor layer, the semiconductor diode absorbing or transmitting the separated monochromatic light according to the magnitude of a reverse bias voltage; And a projection lens for projecting the image formed by being modulated by the modulator toward the screen.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The terms to be described below are terms defined in consideration of functions in the present invention, which may vary depending on the intention or convention of a user or an operator. Therefore, the definitions of these terms should be made based on the contents throughout the specification.

3 is a diagram showing the configuration of a projection system according to an embodiment of the present invention. Referring to the drawings, a projection system includes a light source 110 that illuminates white light, a color filter 115 that separates the white light illuminated from the light source 110 into a plurality of monochromatic light, and the separated monochromatic light, respectively. And a projection lens 125 for projecting an image formed by being modulated by the optical modulator 120 onto a screen.

The white light generated by the light source 110 is incident on the color filter 115, and the color filter 115 is coated with a plurality of filter regions, so that each region transmits only light of a specific wavelength band and does not transmit light of the remaining wavelengths. It is not allowed. The color filter 115 may be divided into, for example, first, second, and third filter regions, and each region may be coated in red, green, and blue. In addition, the color filter 115 is rotated at a high speed to separate the incident white light into red, green, and blue light in time sequence.

The light that is sequentially separated by the color filter 115 and exited is incident on the light modulator 120. A glass rod 117 may be further provided between the light modulator 120 and the color filter 115 to make the light separated from the color filter 115 into uniform light.

The optical modulator 120 serves to modulate the illuminated light according to each color signal. This principle will be described later. The monochromatic light of red, green, and blue is incident on the optical modulator 120 in order to be sequentially modulated, and since the time difference for each color is very short, such a time difference is not recognized by the human eye, and the human eye is recognized as an image formed by combining monochromatic light. do. The image thus formed is projected by the projection lens 125 to reach a screen (not shown).

4 to 7, the structure of the optical modulator employed in the projection system of the present invention, the structure of the semiconductor diode constituting the optical modulator, and the principle of transmitting or absorbing light by the semiconductor diode will be described in detail. do.

FIG. 4 shows an enlarged portion A of the optical modulator shown in FIG. 3 and shows semiconductor diodes 140 arranged in a two-dimensional array.

First, referring to FIG. 4, the semiconductor diode 140 constituting the optical modulator includes a P-type electrode 143 and an N-type electrode 141 so that a reverse bias voltage can be applied, and is arranged in a two-dimensional array. have.

In the two-dimensional array, for example, the N-type electrode 141 of the semiconductor diode 140 positioned in the k-row m-column is arranged in the row direction and has a predetermined potential value, V _{N, k} (k = 1,2,3. Is connected to the N-terminal line (NL _k ). The P-type electrode 143 of the semiconductor diode 140 is arranged in the column direction and has a predetermined potential value, V _{P, m} (m = 1,2,3 ...). _m ).

At this time, the difference (V _{N, k} -V _{P, m} ) of the potential value of each terminal line NL _k, PL _{m to} which the N-type electrode 141 and the P-type electrode 143 is connected is the semiconductor diode 140. Corresponding to the magnitude of the reverse bias voltage (V _R ) applied to). Each semiconductor diode 140 corresponds to one pixel, and as described later, light is turned on or off depending on the magnitude of an applied reverse bias voltage.

The shape of the semiconductor diode 140 including the shapes of the P-type and N-type electrodes is not limited to the illustrated shape, and may be designed in another shape in consideration of image characteristics and the like.

FIG. 5 is a cross-sectional view taken along the line VV ′ of FIG. 4. Referring to the figure, the semiconductor diode 140 has a P-I-N structure of the P-type semiconductor layer 145, the intrinsic semiconductor layer 147, and the semiconductor N layer 149. The P-type electrode 143 and the N-type electrode 141 are formed on the upper portion of the P-type semiconductor layer 145 and the lower portion of the N-type semiconductor layer 149. A transparent electrode 151 is provided between the P-type semiconductor layer 145 and the P-type electrode 143 and between the N-type semiconductor layer 149 and the N-type electrode 141.

For example, a material such as ITO, ZnO, TCO, or NiO may be used as the transparent electrode 151.

When light is incident from the outside, the semiconductor diode 140 absorbs or transmits light depending on the magnitude of the energy of the incident light and the band gap energy of the intrinsic semiconductor layer. That is, the intrinsic semiconductor layer 147 serves as an absorbing layer of light, and is absorbed when the energy of incident light is greater than the band gap energy of the intrinsic semiconductor layer 146, and is transmitted when the intrinsic semiconductor layer 146 is smaller than the band gap energy E _g . The intrinsic semiconductor layer 147 may be formed of a multiple quantum well structure.

On the other hand, the band gap energy has a characteristic of decreasing as the reverse bias voltage increases. When a reverse bias voltage is applied, electric potential energy is added to the energy band. At this time, since the added electric potential energy is different depending on the position, the energy band is inclined and thus the band gap energy is reduced. This is called the quantum-confinement stark effect. As the band gap energy decreases, the energy of incident light absorbed by the intrinsic semiconductor layer 147 also decreases.

7 schematically shows the change in absorption spectrum with reverse bias voltage. The x axis represents the wavelength of incident light and the y axis represents the absorption coefficient (??). [lambda] ₁ , [lambda] ₂ , [lambda] ₃ , and [lambda] ₄ are the minimum wavelengths at which light is not absorbed and starts to be transmitted when the applied reverse bias voltages are -2V, -5V, -8V, and -10V, respectively. As the applied reverse bias voltage increases, the absorption spectrum is shifted to the right. That is, as the reverse bias voltage increases, the minimum wavelength that can pass through the semiconductor diode 140 increases.

By appropriately designing the band gap energy when the reverse bias voltage is not applied and the band gap energy when the reverse bias voltage is applied, light of a specific wavelength band can be turned on / off.

8 is a graph measuring the change in absorption spectrum according to the reverse bias voltage. The semiconductor diode used for the measurement was GaN as the material of the P-type semiconductor layer and the N-type semiconductor layer, and the intrinsic semiconductor layer has a multi-quantum well structure of InGaN / GaN.

Referring to the figure, the wavelength of the transmission band changes as the reverse bias voltage changes from -1V to -20V. When looking at the visible light region (380 nm to 780 nm), which is the band of interest, it can be seen that the minimum wavelength of the transmission band is changed from about 400 nm to 450 nm.

In the case of the structure used in the experiment, light having a wavelength of approximately 400 nm to 450 nm is transmitted through the semiconductor diode when the reverse bias voltage is -1V, and is absorbed when the reverse bias voltage is -20V.

The above experiments are exemplary, and if necessary, by differently designing the structure and material of each semiconductor layer of the semiconductor diode, absorption characteristics may be improved or moved to different wavelength bands.

Since light of red, green, and blue are incident in time to the optical modulator (120 of FIG. 3), the semiconductor diodes (140 of FIG. 4) constituting the optical modulator (120 of FIG. 3) transmit respective monochromatic light to the reverse bias voltage. Should be able to control on / off. That is, it should be possible to control the wavelength of approximately 430nm ~ 650nm band, the minimum wavelength of blue light and the maximum wavelength of red light.

 Since the band gap energy is changed in a direction of decreasing by the reverse bias voltage, the energy band gap energy based on the zero bias is preferably designed to be at least 2.9 eV or more so as to transmit blue light. In addition, the band gap energy is preferably designed to be 1.9 eV or less so that red light is absorbed when the maximum reverse bias voltage is applied.

InGaAlP or InGaAlN-based materials may be used as the intrinsic semiconductor layer serving as the absorption layer.

Meanwhile, absorption of light may occur in the P-type semiconductor layer 144 and the N-type semiconductor layer 148. The P-type semiconductor layer 144 and the N-type semiconductor layer 148 may be designed to transmit light in the visible region in order to effectively turn on / off the light in the intrinsic semiconductor layer that is the absorbing layer. That is, the band gap energy of the P-type semiconductor layer 144 and the N-type semiconductor layer 148 preferably has a value of greater than about 2.9 eV of light energy corresponding to 430 nm, which is the minimum wavelength of blue light.

Each monochromatic light incident on the optical modulator 120 of FIG. 3 is absorbed or transmitted while passing through the intrinsic semiconductor layer according to the reverse bias voltage applied to the semiconductor diode corresponding to each pixel to modulate the light.

The projection system according to the present invention configured as described above is characterized in that configured to perform optical modulation using a semiconductor diode.

In the projection system of the present invention, the semiconductor diode transmits or absorbs light according to the wavelength thereof, and thus, when the semiconductor diode corresponds to the wavelength of the transmission band, the light is transmitted with little loss of light, so that the light efficiency is high and the light modulation speed is high.

In addition, since the one-panel method is adopted, the number of optical parts is reduced, which leads to a more compact and simple structure.

The present inventors' projection system has been described with reference to the embodiments shown in the accompanying drawings for clarity, but this is merely exemplary, and those skilled in the art may various modifications and other equivalent implementations therefrom. It will be appreciated that examples are possible. Therefore, the true scope of protection of the present invention should be defined by the appended claims.

Claims (5)

A light source illuminating white light; and A color filter separating the white light into a plurality of different monochromatic light sequentially in time; and The separated monochromatic light is modulated according to each color signal, and the semiconductor diode is composed of a P-type semiconductor layer, an intrinsic semiconductor layer, and an N-type semiconductor layer to absorb or transmit the separated monochromatic light according to the magnitude of a reverse bias voltage. An optical modulator arranged in units; and And a projection lens for projecting an image modulated by the light modulator toward the screen. The method of claim 1, wherein the optical modulator, And the band gap energy of the intrinsic semiconductor layer is comprised of an array of semiconductor diodes designed to transmit the plurality of monochromatic light when no reverse bias voltage is applied. The method of claim 2, The semiconductor diode of the optical modulator, InGaAlP or InGaAlN as the material of the intrinsic semiconductor layer projection system, characterized in that. The method according to any one of claims 1 to 3, And the P-type semiconductor layer and the N-type semiconductor layer have a band gap energy for transmitting all of the plurality of monochromatic light. The method of claim 4, wherein And a glass rod between the color filter and the light modulator so that the light directed to the light modulator is uniform.

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