KR100437786B1 - Semiconductor Laser Diode - Google Patents

Abstract

The present invention provides a semiconductor laser diode, comprising: a first nitride semiconductor layer, a second nitride semiconductor layer and an electrode having ridge-shaped protrusions on top and bottom of an active layer, and a protective film thickly formed to surround the ridge, in the active layer; The generated optical wave function is prevented from overlapping the electrode to reduce the light absorbed by the metal to improve device characteristics.

Description

Semiconductor Laser Diodes

The present invention relates to a nitride semiconductor laser diode.

Nitride semiconductor laser diodes are being developed and marketed in response to the demands of mass storage devices and color printers. Nitride semiconductor laser diodes require low I _th (threshold current) and high η _ex (external quantum efficiency) for large data storage and color printer applications. The improvement in I _th and η _ex can also reduce heat generation in the device.

At present, in the nitride semiconductor laser diode, an oxide film is stacked beside the ridge as shown in FIG. 1 for passivation of the device.

FIG. 1 shows a cross-sectional view of an upper layer centering on an active layer 1 of a semiconductor laser diode having a ridge structure.

An active layer (1), a p-type waveguide layer (2), a ridge type p-type cladding layer (4), a p-type cap layer (4), a protective film (5) formed on both sides of the ridge type p-type cladding layer (3), and T / P (Transparent Probe) 6 on the top of the p-type cap layer 4, and p-electrode 7 formed on the uppermost portion. When fabricating a nitride semiconductor laser diode device, the protective film 5 is next to the ridge structure. It is formed for passivation with an oxide film such as SiO ₂ .

Currently, in the semiconductor laser diode structure, the ridge portion made of (Al) GaN or the like as the protective film 5 has a large difference in refractive index from SiO ₂ (refractive index n = 1.45 to 1.46), ZrO ₂ (n = 1.97) , SiON (n = ˜1.7) is used.

However, as shown in the simulation graph of the wave function along the cross section of the nitride semiconductor laser diode of FIG. 2, a significant optical wavefunction is applied to the oxide film outside the etched ridge structure regardless of the refractive indices of the oxide films (SiO ₂ , TiO ₂ ). It exists.

That is, when the oxide film is stacked next to the ridge, the optical wave function is considerably present in the oxide film outside the ridge structure, indicating that the distribution of the wave function of the beam generated by the active layer is not significantly affected by the refractive index of the oxide film. Can be.

In general, for the passivation, the oxide film is deposited by sputtering or PECVD, and there is a difficulty in removing I-V characteristics due to plasma damage and removing a thick oxide film due to PR damage.

Due to the lack of understanding of the reason and the effect of the oxide film thickness on the device, conventionally, a thin oxide film is deposited by a passivation process, so that a laser beam in the form of an optical wave function is absorbed by the p-electrode, thereby deteriorating the laser and improving light efficiency. Lowering problem occurs.

Accordingly, the present invention has been made to solve the above problems, the thickness of the protective film such as the oxide film is sufficiently thick to prevent the light from being absorbed by the electrode to minimize the overlapping light and the electrode generated light efficiency is good The purpose is to provide a reliable semiconductor laser diode.

1 is a cross-sectional view of an upper layer centered on an active layer of a semiconductor laser diode having a ridge structure.

2A and 2B are simulation graphs of wave functions along a cross section of a nitride semiconductor laser diode according to the prior art.

* Explanation of symbols for main parts of the drawings

1: active layer

2: p-type waveguide layer

3: ridge structure p-type cladding layer

4: p type cap layer

5: protective film

6: T / P (Transparent Probe)

7: p electrode

Features of the semiconductor laser diode according to the present invention for achieving the above object is an active layer; A first nitride semiconductor layer under the active layer; A second nitride semiconductor layer having a ridge-shaped protrusion on the active layer; A protective film surrounding the ridge and having a lower refractive index than the ridge and having at least one layer thicker; A first electrode connected to the first nitride semiconductor layer; It is configured to include a second electrode formed in connection with the second nitride semiconductor layer.

Preferably, the semiconductor laser diode comprises: an n-type cladding layer, an n-type waveguide layer, an active layer, a p-type waveguide layer, and a p-type cladding layer having ridge-shaped protrusions sequentially formed on a substrate; A protective film surrounding the ridge and having a refractive index lower than that of the ridge and thicker than the at least one layer; A first electrode connected to the n-type cladding layer; It is configured to include a second electrode formed in connection with the p-type cladding layer.

According to an aspect of the present invention, when the protective film is formed to index guiding light on the side of the ridge and prevents damage such as oxidation of the first nitride semiconductor layer or the p-type cladding layer, the protective film is multilayered. Alternatively, by forming a single layer thickly, the light generated in the active layer is prevented from being absorbed by the first electrode formed thereon, thereby preventing an increase in current injected through the first electrode and increasing external quantum efficiency.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

A preferred embodiment of the semiconductor laser diode according to the present invention will be described with reference to the accompanying drawings.

The present invention is applied to all nitride semiconductor laser diodes (InGaN, GaN, AlGaN type) having a ridge structure.

As shown in FIG. 1, the semiconductor laser diode according to the present invention is formed by sequentially stacking n-type GaN (not shown), n-type InGaN (not shown), n-type cladding layer (not shown), n-type waveguide layer (not shown), An active layer (1), a p-type waveguide layer (2), a p-type cladding layer (3) having a ridge, a p-type cap layer (4), and a transparent probe (T / P) on the p-type cap layer (4) ( 6), a protective film 5 formed on both sides of the p-type cladding layer 3, a p-electrode 7 and an n-electrode (not shown) formed on the uppermost portion.

The protective film 5 may use an oxide film around the ridge for passivation, or deposit an oxide film or another material separately from the passivation.

In order to examine the effect of the light generated from the active layer 1 on the nitride semiconductor laser diode of the ridge structure, the optical wavefunction distribution around the ridge structure was examined through simulation.

The simulation of FIGS. 2A and 2B used a commercialization program LASTIP, and Tables 1 and 2 show the parameters of the semiconductor laser diode manufacturing process according to the present invention as an example.

ΔE _c : ΔE _v for InGaN / GaN 3: 7 ΔE _v : ΔE _c for InGaN / GaN 7: 3 Electron mobility of each layer 200cm ² / Vs Hole mobility of p-type waveguide layer 8cm ² / Vs Hole mobility of p-type cladding layer 6 cm ² / Vs Non-radiative Life of the Quantum Well Layer 1ns Non-radiative life of p-type cladding layer 0.1ns Radiation coefficient, B 2 × 10 ^-10 cm ³ / s Mirror loss 47 cm ^-1

layer thickness Carrier Concentration Refractive index p-type cap layer (GaN) 1000Å 5 × 10 ¹⁷ cm ^-3 2.51 p-type cladding layer (Al _0.1 Ga _0.9 N) 4000Å 2 × 10 ¹⁷ cm ^-3 2.46 (Al _0.07 Ga _0.93 N) p-type waveguide layer (GaN) 1000Å 1 × 10 ¹⁷ cm ^-3 2.51 EBL (p-type Al _0.2 Ga _0.8 N) 300 yen 5 × 10 ¹⁶ cm ^-3 2.37 5QWs 2.52 (In _0.02 Ga _0.98 N) 2.56 (In _0.1 Ga _0.9 N) N-type waveguide layer (GaN) 1000Å 1 × 10 ¹⁷ cm ^-3 2.51 n-type cladding layer (A _0.1 lGa _0.9 N) 6000 Å 2 × 10 ¹⁷ cm ^-3 2.46 (Al _0.07 Ga _0.93 N) n-type InGaN 800Å 3 × 10 ¹⁸ cm ^-3 n-type GaN 3 μm 3 × 10 ¹⁸ cm ^-3 2.51

The p-type cladding layer 3 had a thickness of 6000 mV, an etched depth of 6000 mV, a ridge width of 2 m, and an internal loss of 35 cm ^-1 . The ratio of offset used in this simulation was set to ΔE _c : ΔE _v = 3: 7 for InGaN / GaN and ΔE _c : ΔE _v = 7: 3 for InGaN / GaN, which is the closest value to the experimental results.

When SiO ₂ and TiO ₂ are stacked around the ridge, a substantial portion of the optical wave function overlaps with the oxide films such as SiO ₂ and TiO ₂ .

If no oxide film is present or the thickness thereof is thin, an electrode (p electrode) is positioned around the ridge due to the structure of the nitride semiconductor laser diode, and the optical wave function of light generated in the active layer 1 overlaps the electrode. Due to the characteristics of the electrode, light is absorbed by the electrode and generated as heat.

Of course, even in the case where the oscillation wavelength is 400 nm, even if the optical wave function overlaps the electrode, the refractive index of the metal constituting the electrode is small so that the reflection occurs on the surface of the metal, thereby reducing the proportion of the optical wave function overlapping the electrode.

However, in general, when the optical wave function overlaps the electrode, the following two problems occur.

First, as the optical wave function is absorbed by the metal, the overall optical wave function intensity decreases.

Due to such a loss of light, it is necessary to inject a large amount of current to obtain the same light efficiency, thereby increasing I _th and inducing a decrease in η _ex when not injecting a large amount of current.

Secondly, the light absorbed by the metal is generated as heat, which also results in an increase in I _th and a decrease in η _ex .

Therefore, under (1), (2) controlling the thickness of the oxide film as shown in (3) and the thicker the oxide film during the process of the semiconductor laser diode showed an improvement in the breakthrough device characteristics, that is, rapid I _th is reduced and η _ex Increases.

(1) depositing metal around ridges

(2) Depositing a metal (p electrode) after coating 100nm oxide film next to the ridge

(3) deposit 400-500nm oxide film next to ridge and deposit metal (p electrode)

In other words, the thickness of the oxide film beside the ridge should be stacked to the extent that the optical wave function is not absorbed by this metal.

As described above, the semiconductor laser diode according to the present invention, in the ridge type semiconductor laser diode, forms a protective film thickly formed to surround the ridge, thereby preventing the optical wave function generated in the active layer from overlapping the electrode, thereby absorbing light into the metal. By reducing the characteristics of the device is improved.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (3)

Active layer; A first nitride semiconductor layer under the active layer; A second nitride semiconductor layer having a ridge-shaped protrusion on the active layer; A protective film surrounding the ridge and having a refractive index lower than that of the ridge and having a thickness of 100 nm or more and 500 nm or less; A first electrode connected to the first nitride semiconductor layer; And a second electrode connected to the second nitride semiconductor layer. A p-type cladding layer having an n-type cladding layer, an n-type waveguide layer, an active layer, a p-type waveguide layer, and a ridge-shaped protrusion formed sequentially on the substrate; A protective film surrounding the ridge and having a refractive index lower than that of the ridge and having a thickness of 100 nm or more and 500 nm or less; A first electrode connected to the n-type cladding layer; And a second electrode formed in connection with the p-type cladding layer. The method according to any one of claims 1 and 2, A semiconductor laser diode, characterized in that for depositing a metal around the ridge.