HIGH-EFFICIENCY OXIDE VCSEL MANUFACTURING METHOD THEREOF

Abstract

The present invention relates to a vertical cavity surface emitting laser (VCSEL) and a manufacturing method thereof, and more specifically, to a high-efficiency oxidation VCSEL which emits laser beams having a peak wavelength of 860 nm, and a manufacturing method thereof.

Claims

1. An oxide vertical cavity surface emitting laser (VCSEL) having a conductive current spreading layer formed between a top electrode and a top distributed Bragg reflector to pass laser having a peak wavelength of 86010 nm.

2. The VCSEL according to claim 1, wherein the conductive current spreading layer is a non-oxidizing barrier layer.

3. The VCSEL according to claim 2, wherein the non-oxidizing barrier layer is an Al-free layer.

4. The VCSEL according to claim 1, wherein the current spreading layer is a GaP layer.

5. The VCSEL according to claim 1, wherein the GaP layer includes a metallic and/or non-metallic dopant.

6. The VCSEL according to claim 5, wherein the dopant is selected from a group including Mg, Zn and carbon as the dopant.

7. The VCSEL according to claim 5, wherein the GaP layer has a thickness of 1 m or larger.

8. The VCSEL according to claim 1, wherein the VCSEL includes a bottom electrode, a substrate, a bottom distributed Bragg reflector, an active layer, a top distributed Bragg reflector, a top electrode and an oxidized layer.

9. The VCSEL according to claim 8, wherein the active layer is configured of a GaAs quantum well and an AlGaAs quantum barrier layer.

10. The VCSEL according to claim 8, wherein the thickness of the GaP is 3 m.

11. The VCSEL according to claim 8, wherein the oxidized layer is positioned between layers of a top p-DBR.

12. The VCSEL according to claim 8, wherein the oxide CSEL operates at a current of 10 to 40 mA.

13. The VCSEL according to claim 8, wherein the top electrode is a transparent electrode selected among indium tin oxide (ITO), ZnO and AZO.

14. The VCSEL according to claim 8, further including an anti-reflection layer on a top of a current spreading layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 is a view showing an exploded cross-section of a conventional oxide VCSEL.

[0036] FIG. 2(a) is a view showing an SEM image of a DBR damaged when oxidation is progressed, and FIG. 2(b) is a view showing a shape of a current window, in which the black stripe is a trench (pitted) area, and the area in the middle is a pillar area for emitting light, and the brighter area is an oxidized area.

[0037] FIG. 3(a) is a separate cross-sectional view showing a layer structure of an oxide VCSEL according to an embodiment of the present invention, and FIG. 3(b) is a view showing distribution of light emitted from an active layer and light of a resonated laser, (inverse peak is cavity peak).

[0038] FIG. 4 is a view showing the wavelength of an active layer and the cavity peak of an oxide VCSEL according to the present invention.

[0039] FIG. 5 is a graph showing emission intensity when a 20 mA current is applied to (a) a VCSEL without a GaP in comparative example 1, (b) a VCSEL having a GaP of 1 m thick in embodiment 1, (c) a VCSEL having a GaP of 3 m thick in embodiment 2, and (d) a VCSEL having a GaP of 6 m thick in embodiment 3.

[0040] FIG. 6 shows SEM images of the side surfaces of a VCSEL without a GaP layer and 860 nm VCSELs to which GaP barriers of diverse thicknesses are applied and shows mimetic views of current injection paths and light emission.

[0041] FIG. 7 is a view showing (a) an I-V curve and (b) an I-L curve of VCSELs respectively having a thickness of 1, 3 and 6 m in comparative (conventional) example 1 and embodiments 1 to 3 according to application of current of 0 to 50 mA in the present invention.

[0042] FIG. 8 is a graph showing the current-voltage characteristics of a GaP layer and an AlGaAs layer.

TABLE-US-00001 DESCRIPTION OF SYMBOLS 100: Oxide VCSEL 110: Bottom electrode 120: Substrate 130: Bottom DBR 140: Active layer 150: Top DBR 160: GaP layer 170: Top electrode 180: Oxidized layer

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0043] Hereafter, the present invention will be described in detail through embodiments. The embodiments described below are intended not to limit, but to illustrate the present invention.

Embodiments 1 to 3

[0044] FIG. 3 is a view showing a VCSEL layer structure for emitting a laser beam having a peak wavelength of 860 nm, in which a high conductive GaP barrier layer manufactured by a MOCVD system is applied. As shown in FIG. 3, an oxide VCSEL 100 having a peak wavelength of 860 nm, in which a high conductive GaP barrier layer according to the present invention is applied, is an oxide VCSEL 100 which emits laser beams toward the top of a substrate 120. The substrate 120 is an n-type GaAs substrate. A bottom electrode 110 is provided on the lower surface of the substrate 120.

[0045] A bottom n-DBR 130, in which pairs of a high refractive index AlGaAs layer and a low refractive index AlGaAs layer are repeatedly stacked, is provided on the top surface of the substrate 120. An Al.sub.0.85Ga.sub.0.15As layer and an Al.sub.0.15Ga.sub.0.85As layer are repeatedly stacked as many as forty times.

[0046] An active layer 140 is provided on the bottom DBR 130. The active layer 140 includes a quantum well structure for generating light. The active layer 140 is a GaAs/AlGaAs active layer QW for emitting light having a center wavelength of 850 nm.

[0047] A top p-DBR 150 including an oxidized layer 180 is provided on the active layer 140. To avoid damage of the active layer in an oxidization process, the oxidized layer 180 may be inserted between layers of the pairs configuring the p-DBR 150 and may avoid direct contact with the active layer 140. The active layer 140 is stacked on a pair or two pairs of the top DBRs among the twenty pairs, and the other pairs of the top DBR are stacked on the oxidized layer 180.

[0048] Accordingly, the top DBR 150 is configured of a first top DBR 151 positioned on the bottom of the oxidized layer 180 and a second top DBR 152 positioned on the top of the oxidized layer 180.

[0049] In the same manner as the bottom n-DBR, pairs of a high refractive index AlGaAs layer and a low refractive index AlGaAs layer are repeatedly stacked in the top p-DBR 150, and the top p-DBR 150 is configured of twenty pairs of an Al.sub.0.85Ga.sub.0.15As layer and an Al.sub.0.15Ga.sub.0.85As layer.

[0050] The oxidized layer 180 is configured of a circular current window (oxidation aperture) 181 formed of Al.sub.0.98Ga.sub.0.02As having a thickness of about 30 nm at the center and an oxidized ring 182 at the periphery. The DBR reflectivity shows an excellent characteristic of the stop-band shape at almost 98%.

[0051] A GaP layer 160 is grown on the top p-DBR 150 in the MOCVD method. As shown in FIG. 4, the GaP layer is grown as much as about 1 m (embodiment 1), 3 m (embodiment 2) and 6 m (embodiment 3), respectively. A top electrode 170 is formed on the top GaP 160 in a ring shape. The peak wavelength of the active layer 140 is about 850 nm, and the cavity peak is about 860 nm by the DBR reflection.

COMPARATIVE EXAMPLE 1

[0052] In the embodiments 1 to 3, the top electrode 170 of a ring shape is formed on the top p-DBR 150 without a GaP layer 160.

[0053] Test

[0054] A 20 mA current is applied to a VCSEL without a GaP layer (comparative example 1) and VCSELs to which a GaP barrier having a thickness of 1, 3 and 6 m is applied (embodiments 1, 2 and 3), and emission intensity is measured. Its result is shown in FIG. 5.

[0055] It is confirmed that in the case of a general VCSEL to which a GaP layer is not applied, an intensity of about 0.45 is shown, and the characteristic of low intensity is improved considerably according to application of a GaP barrier and increase in the thickness thereof. When a GaP barrier having a thickness of 1 m is applied, the intensity is 0.78, which is an increase of about 50% compared with the VCSEL to which the GaP layer is not applied.

[0056] Particularly, it is confirmed that when a GaP barrier having a thickness of 3 m is applied, the intensity is 0.94, showing an increase of about 90%. In addition, it is confirmed that when a GaP barrier having a thickness of 6 m is applied, the emission intensity is 0.94, showing an increase of about 90%. When a VCSEL to which a GaP barrier of 3 m or larger is applied, a characteristic almost the same as that of the emission intensity is shown with the increase of thickness, and this is a saturation phenomenon of the emission intensity according to thickness and is determined as having been controlled by a 10 m diameter of the current window. It is confirmed from this result that application of a GaP barrier greatly increases light efficiency of the 860 nm VCSEL, and it is confirmed that thickness of the GaP barrier is optimized by the oxidation aperture diameter of the VCSEL.

[0057] FIG. 6 shows SEM images of the side surfaces of a VCSEL without a GaP layer and 860 nm VCSELs to which GaP barriers of diverse thicknesses are applied and shows mimetic views of current injection paths and light emission.

[0058] It is confirmed from the SEM images of FIG. 6 that the GaP barrier is normally grown on the top of the DBR at a thickness of about 1 m, 3 m and 6 m. The current injection path and the light emission effect of a VCSEL structure according to application of a GaP barrier can be confirmed from the mimetic view, and in the case of a VCSEL without a GaP barrier (comparative example 1), a small light emission area is generated along the edge of the limited oxidation layer, in which the current injection path is limited by the current window when current is applied, and accordingly, only a small light emission effect is confirmed.

[0059] On the contrary, the current injection path continuously increases when the GaP barrier is applied and the thickness increases, and accordingly, it is confirmed that the light emission area continuously increases, and in addition, the light emission effect is also abruptly enhanced.

[0060] Through the mimetic view of the rightmost current injection path and light emission, it is understood that the light emission effect cannot be expected any more when the light emitting area is saturated in an area in which the GaP barrier effect is already limited by the current window at a predetermined thickness. Such a result may support the emission intensity result of FIG. 5.

[0061] FIG. 7 is a view showing (a) an I-V curve and (b) an I-L curve of VCSELs developed according to application of current 0 to 50 mA in the present invention.

[0062] Confirming the (a) I-V characteristic, the I-V characteristics of all the samples are the same without regard to application of a GaP barrier. This is since that conductivity of the GaP is relatively high compared with those of VCSEL materials. On the contrary, confirming the (b) I-L characteristic, it is understood that the light efficiency characteristic is changed significantly according to application of the GaP barrier and change in the thickness thereof.

[0063] It is confirmed that light efficiency of a general VCSEL of comparative example 1 is about 17 mW at about 33 mA. When a GaP barrier having a thickness of 1 m is applied as shown in embodiment 1, light efficiency is about 22.5 mW, which is an increase of about 25%, and when a GaP barrier having a thickness of 3 m is applied as shown in embodiment 2, light efficiency is about 26 mW, which is an increase of about 40%, and when a GaP barrier having a thickness of 6 m is applied as shown in embodiment 3, light efficiency is the same as that of applying a GaP barrier having a thickness of 3 m.

[0064] As a result, light efficiency of an 860 nm VCSEL having an oxidation aperture of about 10 m diameter can be enhanced greatly by the high conductive GaP barrier applied to grow on the top p-DBR, and highest light efficiency can be obtained by a GaP barrier optimized at a thickness of about 3 m.

[0065] According to the present invention, there is provided a new barrier, which is also a current spreading layer, capable of protecting a top DBR in an oxidization process, enhancing flow of current, and passing light of an 860 nm VCSEL.

[0066] The oxide VCSEL having a GaP barrier layer according to the present invention enhances light efficiency up to 40% by improving electrode protection and current flow of an 860 nm VCSEL having an oxidation aperture, and an optimum range of efficiency between the applied high conductive material and the oxidation aperture of the VCSEL can be confirmed.

[0067] Although the present invention has been illustrated and described in detail in the above drawings and descriptions, it is considered that the drawings and descriptions are illustrative or exemplary and not restrictive. Other changes may be apparent to those skilled in the art from the present invention. These changes may accompany other features that can be used instead of or in addition to the features publicized in this field or described in this specification. Modifications of the disclosed embodiments may be understood and affected by those skilled in the art from learning of the drawings, the present invention and the appended claims. The term comprising used in the claims does not exclude other elements or steps, and description of an indefinite article does not exclude a plurality of elements or steps. The fact that particular actions are cited in different dependent claims does not mean that these actions cannot be used to make combinations of the actions advantageous. Arbitrary reference symbols in the claims should not be interpreted as limiting the scope of the claims.