KR20180089174A - Apparatus and method for detecting surface defect of light emitting diode - Google Patents

Abstract

According to an embodiment of the present invention, disclosed is an apparatus for detecting a surface defect of a light emitting element which comprises: a light source unit for irradiating a light emitting element with first light; a detection unit for detecting photoluminescence light emitted by the light emitting element; and a control unit for communicating with the light source unit and the detection unit. The light emitting element includes an n-type semiconductor layer, an active layer, and a p-type semiconductor layer. The control unit measures surface defect information of the p-type semiconductor layer by measuring an intensity rate of photoluminescence light of the p-type semiconductor layer and photoluminescence light of the active layer. The apparatus can nondestructively detect a surface defect of the light emitting element.

Description

[0001] APPARATUS AND METHOD FOR DETECTING SURFACE DEFECT OF LIGHT EMITTING DIODE [0002]

An embodiment relates to an apparatus and a method for measuring surface defects of a light emitting device.

Defects in nitride semiconductors degrade the electrical and optical properties of nitride semiconductor structures and related semiconductor devices. In nitride semiconductors, defect levels exist inside the bandgap, which has already been theoretically and empirically proven.

When a photoluminescence is actually measured with respect to a nitride semiconductor, a luminescence having a wide width at around 550 nm is observed, which is called yellow luminescence. Unlike band gap luminescence, yellow luminescence is luminescence from the subband gap, but it is unnecessary luminescence in the light side.

Generally, yellow luminescence is observed when luminescence of n-type GaN or undoped GaN is measured. The cause may be attributed to the transition of the deep acceptor and shallow donor levels formed by the Ga vacancy. The Ga vacancy is a representative defect of GaN, which refers to a vacancy where Ga is vacated when Ga and N form GaN crystal. In order to grow high-quality GaN crystals, it is necessary to minimize the point defects such as Ga vacancy.

Separately, the GaN surface defects also form acceptor levels, which in turn emit yellow luminescence as a result of shallow donor-deep acceptor transitions. Surface defects are defects present on the surface. Defects inside the thin film may be formed by moving to the surface, or dangling bonds remaining in an unbound state on the surface may act as surface defects.

In the light emitting diode structure, the p-type GaN is located on the surface of the p-type GaN surface, and there is a dangling bond remaining on the p-type GaN surface in an unbonded state.

Dangling bonds are surface defects that occur when atoms do not bond normally, and energy levels are present in the subband gaps inside the bandgap, which can cause yellow luminescence.

The dangling bond is a surface bond that is always formed on the surface of the sample, so that a dangling bond is naturally formed on the GaN surface. However, when Mg is doped, the formation of the dangling bond is further promoted. Therefore, in the case of a light emitting diode structure in which p-type GaN is located on the surface, it is necessary to pay attention to the formation of dangling bonds and to minimize the light loss.

In addition, in the light emitting diode structure, the p-type GaN surface defects increase not only the yellow luminescence but also the contact resistance during the fab process, thereby increasing the operating voltage. Therefore, the surface defects must be minimized also for the electrical characteristics of the chip.

Therefore, it is important to analyze the surface defects of the p-type GaN at the process step of the light emitting diode or after the process is completed by an optical method which is a nondestructive analysis.

The embodiment provides a measuring apparatus and method thereof capable of non-destructively measuring surface defects of a light emitting element.

The problems to be solved in the embodiments are not limited to these, and the objects and effects that can be grasped from the solution means and the embodiments of the problems described below are also included.

An apparatus for measuring surface defects according to an embodiment of the present invention includes: a light source unit for emitting first light to a light emitting element; And a detector for measuring the photoluminescence light emitted by the light emitting element; And a control unit for communicating with the light source unit and the detection unit, wherein the light emitting device includes an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, wherein the control unit controls the photoluminescence light of the p- The surface defect information of the p-type semiconductor layer is calculated by calculating the intensity ratio of the photoluminescence light of the p-type semiconductor layer.

According to the embodiment, surface defects of the p-type semiconductor layer of the light emitting element can be measured.

The various and advantageous advantages and effects of the present invention are not limited to the above description, and can be more easily understood in the course of describing a specific embodiment of the present invention.

1 is a conceptual diagram of a surface defect measuring apparatus according to an embodiment of the present invention,
2 is a conceptual diagram of a light emitting element which is an object to be measured,
Fig. 3 is a modification of Fig. 2,
4 is a graph showing a change in yellow luminescence according to a change in intensity of a laser,
5 is a table for measuring the ratios of the luminescence of the p-type semiconductor layer and the luminescence of the active layer with respect to the change in the laser intensity,
6 is a graph showing the intensity ratios of various samples,
7 is a flowchart of a surface defect measurement method according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the embodiments of the present invention are not intended to be limited to the specific embodiments but include all modifications, equivalents, and alternatives falling within the spirit and scope of the embodiments.

Terms including ordinals, such as first, second, etc., may be used to describe various elements, but the elements are not limited to these terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the embodiments, the second component may be referred to as a first component, and similarly, the first component may also be referred to as a second component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings, wherein like or corresponding elements are denoted by the same reference numerals, and redundant description thereof will be omitted.

1 is a conceptual diagram of a surface defect measuring apparatus according to an embodiment of the present invention.

1, a surface defect measuring apparatus according to an embodiment of the present invention includes a light source unit 10 that emits a first light L1 to a light emitting device 100, a light source unit 10 that emits the first light L1 A detector 30 for measuring the emitted photoluminescence light L2 and a controller 60 for communicating with the light source 10 and the detector 30.

The light source unit 10 may include a light source 11 that emits the first light L1 of a predetermined wavelength and at least one reflective mirror 12 and 13 that changes the path of the first light L1. The type of the light source 11 is not particularly limited. Illustratively, the light source unit 10 may be a laser diode or a light emitting diode.

The wavelength range of the first light L1 may be 200 nm to 365 nm. When the wavelength band is smaller than 200 nm or larger than 365 nm, it is difficult to measure the photoluminescence of the p-type semiconductor layer.

The intensity of the first light (L1) may be 0.005W / cm ² to 5.0W / cm ^2. If the strength is less than 0.005W / cm ² when there is a problem that noise is generated a measurement error becomes large is higher than 5.0W / cm ² intensity, there is a problem in that the photo-luminescence of the p-type semiconductor layer is not observed.

The intensity adjusting unit 14 may be disposed between the light source unit 10 and the light emitting device 100 to change the intensity of the first light L1. Illustratively, the power setting unit 14, the intensity may be adjusted step by step weaken the intensity of the first light (L1) within a range of 0.01W / cm ² to 5.0W / cm ^2. Illustratively initially controls the first light (L1) to 5.0W / cm ^2, and the intensity at a predetermined interval can be adjusted so that the ^{0.1W / cm 2, 0.05W / cm} 2, and 0.025W / cm ² . However, the present invention is not limited thereto, and the strength and the number of times may be appropriately modified.

The configuration in which the intensity adjusting section 14 changes the intensity of the first light L1 is not particularly limited. By way of example, the intensity of the light can be adjusted by adjusting the reflectivity, or the intensity can be adjusted by absorbing a part of the light. A chopper 15 may be disposed between the intensity controller 14 and the light source 11. Only the luminescence due to the laser passing through the chopper 15 can be measured.

The filter 21 can reflect the first light L1 and enter the surface of the light emitting device 100 disposed in the holder 22. [ Also, the filter 21 can transmit the photoluminescence light L2 emitted from the light emitting device 100. The filter 21 may be selected from various kinds of optical mirrors that transmit and reflect the light according to the wavelength of the light.

The detector 30 can measure the photoluminescence light. At this time, the detector 30 can measure the photoluminescence of the active layer and / or the photoluminescence of the p-type semiconductor layer according to the intensity of the first light L1. Illustratively, the detector 30 may be a light pipe (PMT). Conventionally, the detector 30 for measuring the photoluminescence uses a CCD having a high measuring speed, but in this case, there is a problem that the level of yellow luminescence can not be detected. A spectroscope 40 may be disposed between the detector 30 and the filter 21. The spectroscope 40 can perform a function of separating the luminescence in which a plurality of wavelengths are mixed, by wavelength.

That is, since the embodiment uses the first light having a very low intensity, the intensity of the luminescence can also be very small. Therefore, it is necessary to use an optical radiation pipe having excellent sensitivity.

The amplifier 50 is capable of amplifying the signal detected by the detector 30. Amplifier 50 may be, but is not necessarily limited to, a digital lock-in amplifier. The amplifier 50 can amplify the signal of the detector 30.

The control unit 60 can calculate the intensity ratio of the photoluminescence of the p-type semiconductor layer and the photoluminescence of the active layer detected by the detector 30. [ The degree of surface defects of the p-type semiconductor layer can be determined.

Fig. 2 is a conceptual diagram of a light emitting element which is an object to be measured, and Fig. 3 is a modification of Fig.

2, the light emitting device 100 includes a substrate 110, a buffer layer 111, a first conductive semiconductor layer 124, an active layer 126, and a second conductive semiconductor layer 127 .

The first conductive semiconductor layer 124 may be formed of a compound semiconductor such as Group III-V or Group II-VI, and the first dopant may be doped. The first conductive semiconductor layer 124 may be a semiconductor material having a composition formula of In _{x 1} Al _{y 1} Ga ₁ -x ₁ -y1 N (0? _{X1? 1} , 0 _{? Y1? 1} , 0? X1 + y1? For example, GaN, AlGaN, InGaN, InAlGaN, and the like. The first dopant may be an n-type dopant such as Si, Ge, Sn, Se, or Te. When the first dopant is an n-type dopant, the first conductivity type semiconductor layer 124 doped with the first dopant may be an n-type semiconductor layer.

The active layer 126 may be disposed between the first conductive semiconductor layer 124 and the second conductive semiconductor layer 127. The active layer 126 is a layer where electrons (or holes) injected through the first conductive type semiconductor layer 124 and holes (or electrons) injected through the second conductive type semiconductor layer 127 meet. The active layer 126 transitions to a low energy level as electrons and holes recombine, and can generate light having ultraviolet wavelengths.

The active layer 126 includes a well layer 126a and a barrier layer 126b and may include a single well structure, a multiple well structure, a single quantum well structure, a multi quantum well (MQW) structure, a quantum dot structure, , And the structure of the active layer 126 is not limited thereto.

The second conductive semiconductor layer 127 may be formed on the active layer 126 and may be formed of a compound semiconductor such as a group III-V or a II-VI group. In the second conductive semiconductor layer 127, The dopant can be doped. A second conductive semiconductor layer 127 is a semiconductor material having a compositional formula of _{In x5 Al y2 Ga 1 -x5- y2} N (0≤x5≤1, 0≤y2≤1, 0≤x5 + y2≤1) or AlInN , AlGaAs, GaP, GaAs, GaAsP, and AlGaInP. When the second dopant is a p-type dopant such as Mg, Zn, Ca, Sr, or Ba, the second conductivity type semiconductor layer 127 doped with the second dopant may be a p-type semiconductor layer.

Referring to FIG. 3, the first electrode 142 and the second electrode 246 may be ohmic or pad electrodes. The first electrode 142 and the second electrode 246 may be formed of one selected from the group consisting of ITO (indium tin oxide), IZO (indium zinc oxide), IZTO (indium zinc tin oxide), IAZO (indium aluminum zinc oxide), IGZO ), IGTO (indium gallium tin oxide), AZO (aluminum zinc oxide), ATO (antimony tin oxide), GZO (gallium zinc oxide), IZON (IZO Nitride), AGZO ZnO, ZnO, IrOx, RuOx, NiO, RuOx / ITO, Ni / IrOx / Au or Ni / IrOx / Au / ITO, Ag, Ni, Cr, Ti, Al, Rh, Pd, Ru, Mg, Zn, Pt, Au, and Hf. However, the present invention is not limited to these materials.

In a general PL measuring apparatus, the intensity of the light source is high, so that the photoluminescence of the p-type semiconductor layer is not observed. In addition, the p-type semiconductor layer is as thin as about 50 nm to 200 nm, and may not be excited even when light is absorbed. In this respect, the embodiment is distinguished from most PL measuring apparatuses which measure the luminescence of the active layer by increasing the intensity of light.

FIG. 4 is a graph showing the change in the yellow luminescence according to the change in the intensity of the laser, and FIG. 5 is a graph showing the intensity ratio between the luminescence of the p-type semiconductor layer and the luminescence of the active layer, .

Referring to FIG. 4, only the luminescence P1 of the active layer is detected and the luminescence P2 of the p-semiconductor layer is not detected when the laser intensity is output at 5.0 W / cm ² . Next, it can be seen that the luminescence (P2) of the p-type semiconductor layer is not detected even when a laser of 0.1 W / cm ² is output. However, it can be seen that the luminescence (P2) of the p-type semiconductor layer is detected when a laser of 0.05 W / cm ² is output. In addition, it can be seen that the luminescence (P2) of the p-type semiconductor layer is detected more strongly when a laser of 0.025 W / cm ² is output. Thus, 0.01 W / cm ² 0.1 W / cm < ² > It can be seen that the luminescence of the p semiconductor layer can be measured by irradiating a laser of a smaller intensity.

Referring to FIG. 5, the laser intensity was adjusted to 5.0 W / cm ² , 0.1 W / cm ² , 0.05 W / cm ² and 0.025 W / cm ² , , It can be seen that the intensity ratio increases nonlinearly as the intensity of the first light L1 decreases.

At this time, the degree of surface defect can be confirmed by substituting the measured intensity ratio into the following relational expression (1).

[Relation 1]

Here, R is the intensity of the luminescence ratio of the luminescence and the active layer of the p-type semiconductor layer, I is the intensity of the first light (L1), R ₀ is a group prepared (reference ratio), A1 has surface defects And A2 is the slope. Here, A1 is a factor for determining surface defects, and the larger the value is, the more surface defects can be interpreted. R ₀ , A 1 and A 2 can be calculated by fitting automatically using various calculation programs (eg origin, excel). Therefore, the surface defect index A 1 can be obtained.

Fig. 6 is a table for measuring intensity ratios of various samples.

As a result of experimenting three samples having different Mg doping concentrations of the P-type semiconductor layer, a fitting graph as shown in FIG. 6 was obtained. In the first embodiment, the doping concentration of the p-type semiconductor layer is 1.2 x 10 ²⁰ cm / 3, the doping concentration of the p-type semiconductor layer is 1.8 x 10 ²⁰ cm / 3 in the second embodiment, Type semiconductor layer has a doping concentration of 2.5 x 10 < ²⁰ > cm / 3. The remaining epilayer was made identically. As a result of the calculation, the values of the parameters can be obtained as follows.

Example 1 Example 2 Example 3 Ro 0.068 0.066 0.088 A1 3.61 11.33 23.89 A2 0.018 0.014 0.013

Referring to this, it can be seen that the Al value of Example 3 having the highest Mg doping concentration is the largest. Therefore, it can be judged that the surface defect of Example 3 is the largest. According to the embodiment, the degree of surface defects of the light emitting diode can be calculated by fitting the measured values and calculating A1.

In each of the embodiments, only the doping concentration of the p-type semiconductor layer was controlled differently, and the other conditions were the same. Therefore, it can be judged that the samples having different intensity ratios according to the embodiments are related to the doping concentration of the p-type semiconductor layer. That is, it can be judged that the yellow luminescence having the energy of about 2.2 eV (wavelength of 550 nm) is caused by surface defects of the p-type semiconductor layer.

However, the degree of surface defects can be calculated by various methods without being limited thereto. Illustratively, the memory of the measuring apparatus can store the surface defect information of the p-type semiconductor layer in accordance with the luminescence of the p-type semiconductor layer and the luminescence intensity ratio of the active layer. Accordingly, the controller 60 may calculate the intensity ratio and then read the surface defect value matched in the table value.

7 is a flowchart of a surface defect measurement method according to an embodiment of the present invention.

Referring to FIGS. 1 and 7, a surface defect measurement method according to an embodiment of the present invention includes the steps of irradiating a first light L1 to a light emitting device 100 including an n-type semiconductor layer, an active layer, and a p- , Calculating the intensity ratio of the photoluminescence light of the p-type semiconductor layer emitted from the light emitting element (100) and the photoluminescence light of the active layer, and calculating the intensity ratio of the photoluminescence light of the active layer And determining the degree of defect.

In the step S11 of irradiating the first light L1, when the p-type electrode is disposed in the light emitting element 100, light can be irradiated to the p-type semiconductor layer on which the p-type electrode is not disposed.

The first light L1 can irradiate light a plurality of times by adjusting the intensity of light. Illustratively, the first light L1 can be irradiated at an intensity of 5.0 W / cm ² , 0.1 W / cm ² , 0.05 W / cm ² , and 0.025 W / cm ² to measure the luminous intensity ratio. However, the intensity and frequency of each light can be appropriately adjusted.

The step of calculating the intensity ratio (S12) can calculate the intensity ratio of the photoluminescence light of the p-type semiconductor layer and the photoluminescence light of the p-type semiconductor layer. The intensity ratio can calculate the intensity ratio measured according to the intensity of light.

The step of determining the degree of surface defects of the p-type semiconductor layer (S13) can quantify the surface defects of the p-type semiconductor layer in accordance with the intensity ratio. As described above, the degree of surface defects can be determined using the relational expression 1, or the degree of surface defects can be determined using the information stored in the memory.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood that various modifications and applications are possible. For example, each component specifically shown in the embodiments can be modified and implemented. It is to be understood that all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (8)

A light source unit for emitting the first light to the light emitting element; And
A detector for measuring the photoluminescence light emitted by the light emitting element; And
And a control unit for communicating with the light source unit and the detection unit,
Wherein the light emitting element includes an n-type semiconductor layer, an active layer, and a p-type semiconductor layer,
Wherein the control section calculates the intensity ratio of the photoluminescence light of the p-type semiconductor layer and the active layer to the surface defect information of the p-type semiconductor layer.
The method according to claim 1,
And an intensity adjusting unit disposed between the light source and the light emitting device to change the intensity of the first light.
The method according to claim 1,
Wherein the control section calculates the intensity ratio of the photoluminescence light of the active layer and the photoluminescence light of the p-type semiconductor layer separately from the intensity of the first light.
The method according to claim 1,
Surface defects measuring device of the light-emitting element 1, light intensity range is 0.005W / cm ² to 5.0W / cm ² which is output from the light source.
The method according to claim 1,
And a memory for storing surface defect information of the p-type semiconductor layer according to the intensity ratio,
Wherein the controller calculates surface defect information of the p-type semiconductor layer according to the intensity ratio using information stored in the memory.
irradiating a first light to a light emitting device including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer;
Calculating the intensity ratio of the photoluminescence light of the p-type semiconductor layer emitted from the light emitting element and the photoluminescence light of the active layer; And
And determining the degree of surface defects of the p-type semiconductor layer according to the intensity ratio.
The method according to claim 6,
Wherein the step of irradiating the first light comprises:
And irradiating the light emitting element with the intensity of the first light gradually lowered.
8. The method of claim 7,
The step of calculating the intensity ratio may include:
The intensity ratio of the first light to the active layer is lowered stepwise to measure the intensity ratio of the photoluminescence light of the p-type semiconductor layer and the photoluminescence light of the active layer, respectively.

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