JPH1065212A - Nitride-based compound semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the p-side contact resistance and the operating voltage of an element by forming a contact layer on an active layer, through a clad layer and composing the contact layer of a nitride-based compound semiconductor containing Si and C at a specified ratio. SOLUTION: An n-GaN layer 11, an n-Al0.2 Ga0.8 clad layer 12, an In0.15 Ga0.85 N active layer 13, and a p-Al0.2 Ga0.8 N clad layer 14 are formed sequentially on a sapphire substrate 10. An Mg doped (GaN)0.8 (SiC)0.2 contact layer 15 is then formed, while containing Si and C at a ratio of 1:1. Subsequently, a p-side electrode 16 and an n-side electrode 17 are formed. Since Si and C are added at a ratio of 1:1 to GaN, and an Mg doped layer is employed as the contact layer, activation rate of Mg is enhanced and the contact resistance is decreased. Furthermore, lattice mismatch difference is mostly eliminated with respect to the p-Al0.2 Ga0.8 N clad layer 14, and the interface characteristics are enhanced also.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device comprising a nitride-based compound semiconductor, and in particular, to GaN, AlGaN,
The present invention relates to a semiconductor device such as a semiconductor light emitting device made of a nitride-based compound semiconductor using InGaN or the like.

[0002]

2. Description of the Related Art In recent years, a semiconductor laser (LD) capable of emitting light at a short wavelength has been required in order to improve the recording density of an optical disk and the resolution of a laser printer. As a short wavelength semiconductor laser made of InGaAlP material 6
The characteristics of the 00 nm band light emitting device have been improved to the level that can be used as a light source for reading and writing to a disk, and the device has already been put to practical use. However, the blue semiconductor laser has been actively developed with the aim of further increasing the recording density. ing.

In such development, a blue-green semiconductor laser using a ZnSe-based material, which is a II-VI group compound semiconductor, has been developed for practical use such as prolonging its life and improving reliability since its oscillation operation was confirmed. Is being actively conducted.
However, in this material system, dislocations caused by a lattice mismatch difference and a difference in thermal expansion coefficient between the growth substrate and the growth layer having the element portion multiply due to energization, so that reliability cannot be obtained. It has been found that barriers to practical use, such as a short lifetime, are high.

On the other hand, a GaN-based semiconductor laser is expected to be a promising material because it can be further shortened in wavelength as compared with a ZnSe-based material, and is also harder in terms of reliability than a ZnSe-based laser. I have. Reliability of more than 10,000 hours has been confirmed for LEDs using this material system. Currently, research and development of blue semiconductor lasers that satisfy the conditions required for light sources for next-generation optical disk systems have been actively conducted. I have.

[0005]

However, GaN-based LDs
Is not as easy as the realization of LEDs, and some problems must be solved. One of the reasons why laser oscillation is difficult in this material system or the reliability of the element cannot be obtained by laser oscillation is the problem of the p-side electrode. At present, since the contact resistance of the p-side electrode is high, the operating voltage of the element is high, and laser oscillation is difficult. Therefore, to realize a GaN-based semiconductor laser, it is essential to reduce the p-side contact resistance.

Conventionally, to solve this problem, GaN
The contact resistance was reduced by doping the crystal with a p-type dopant such as Mg.However, when the p-type dopant reaches a certain concentration, the resistance value does not decrease even if the concentration is further increased. Was seen. The reason why such a phenomenon occurs is that GaN has a large band gap energy of about 3.4 eV at 300 K, and GaN has a strong ionic bond (Phillips, which shows a strong ionic bond, has an ionicity of 0.500. ) For Mg
Is presumed to be difficult to activate. In other words, when Mg is doped at a high concentration into GaN having a high ionic bondability, although Mg is taken into GaN, the neutral condition of charge is maintained by inducing defects,
It is considered that the activation rate as a p-type carrier concentration is as low as about 1% with respect to the Mg concentration in GaN and does not contribute to lowering the resistance of the p-type contact layer.

The present invention has been made in view of such circumstances, and it has been made possible to reduce the p-side contact resistance of a GaN-based light emitting device, reduce the operating voltage of the device, facilitate laser oscillation, and It is an object of the present invention to provide a highly reliable semiconductor light emitting device having a significantly increased device life.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a method for forming a first substrate on a substrate.
An active layer formed on the active layer, a contact layer formed on the active layer via a second clad layer, a first electrode formed on the contact layer, and a first electrode formed on the contact layer. A second electrode provided on the opposite side of the active layer with respect to the first electrode and the second electrode.
And C in a one-to-one ratio.

Further, according to the present invention, the contact layer or the second cladding layer may be formed of a nitride-based compound semiconductor containing at least one of Ga, Al, In, and B and N.
i and C comprises in a ratio of _{1-to-1, (Ga a Al b In} c B
_dN ) _1-x (SiC) _x (where a + b + c + d =
1, 0 ≦ a, b, c, d ≦ 1, 0 <x <1).

[0010] Further, the present invention provides the first or second aspect.
Is characterized in that the cladding layer is made of a compound semiconductor containing Si and C in a nitride compound semiconductor at a ratio of 1: 1.

Further, the present invention provides an active layer formed on a substrate via a first clad layer, a contact layer formed on the active layer via a second clad layer, and a contact layer formed on the active layer via a second clad layer. In a nitride-based compound semiconductor device comprising a first electrode formed thereon and a second electrode provided on the opposite side of the active layer with respect to the first electrode, the contact layer may be made of SiC. Is characterized by the following.

Further, according to the present invention, there is provided an active layer formed on a substrate via a first clad layer, and a second layer formed on the active layer.
A contact layer formed on the contact layer, a first electrode formed on the contact layer, and a second electrode provided on the opposite side of the active layer with respect to the first electrode. Wherein the contact layer is formed by alternately stacking a nitride-based compound semiconductor layer and a compound semiconductor layer containing Si and C at a ratio of 1: 1. A nitride-based compound semiconductor light-emitting device is obtained.

That is, according to one embodiment of the present invention,
The ratio of Si and C to GaN is 1: 1 to 20
By using a layer doped with Mg in a compound (GaN) _0.8 (SiC) _0.2 containing _0.2 % as a contact layer, M
The activation rate of g was greatly improved, and the resistance of the contact layer could be significantly reduced. This is because
SiC has a band gap energy of 2.8 at 300K.
6 eV, which is smaller than that of GaN, and whose ionicity of Philips indicating the strength of ion bonding is 0.500 of GaN.
This is considered to be because the p-type dopant, which is hardly activated by GaN, is easily activated because it is as small as 0.177.

The present invention can improve the activation rate of a p-type dopant when applied to a p-type cladding layer in a light emitting device of the same material as well as a p-type contact layer. It can also be applied to increase the activation rate.

According to the present invention, the resistance of the contact layer with the p-side electrode and the p-type and n-type clad layers can be reduced.
It is possible to provide a semiconductor light emitting device in which the operating voltage of a laser device or a light emitting diode device can be reduced and reliability and device life are improved.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing a basic structure of a semiconductor light emitting device of the present invention in comparison with a conventional structure. FIG. 1A shows a layer structure according to the conventional technology, and FIG. 3 shows a layer structure. In this embodiment, p-type doping was performed on GaN (gallium nitride) in order to determine the growth conditions of the contact layer for the p-side electrode for the nitride-based blue semiconductor laser, and an experiment was conducted to examine the doping characteristics.

First, a Mg-doped GaN layer was formed by using Cp ₂ Mg (biscyclopentadienyl magnesium) as a dopant in the GaN layer as in the conventional method, and the electrical characteristics thereof were examined. As shown in FIG. 1A, undoped GaN is used as a base layer on a sapphire substrate 1 via a low-temperature GaN buffer layer 2 (growth temperature of 550 ° C.) by metal organic chemical vapor deposition (MOCVD). Layer 3 for 1 hour (~ 2
μm), and n-GaN layer 4 is grown thereon by using SiH ₄ (silane) as a dopant for 1 hour (〜
2 μm) at a growth temperature of 1150 ° C. On top of that, a p-GaN layer 5 (Mg-doped, 3-5 × 10 ¹⁸ c
m ⁻³ ) was formed for 10 minutes (〜0.3 μm), and the obtained sample was heat-treated at 750 ° C. in a nitrogen atmosphere for 30 minutes to activate Mg in the GaN layer.

The p-GaN layer 5 thus obtained is subjected to secondary ion mass spectrometry (SIMS)
When the concentration of Mg in the aN layer was examined, it was found to be about 3 × 10 ¹⁹
cm ^-3 . Next, the acceptor concentration and the carrier concentration of this sample were evaluated by capacitance-voltage (CV) measurement and Hall effect measurement. As a result, the acceptor concentration was 8 × 10 ¹⁷ cm ⁻³ and the p-type carrier concentration was 3 × 10 ^17
17 cm ^-3 , and the activation rate of Mg as a carrier was 1
% Was confirmed to be low.

Next, according to the present invention, instead of the p-GaN layer, bis-trimethylsilylmethane (BTMS)
M (CH ₃ ) ₃ —Si—CH ₂ — (CH ₃ ) ₃ ] at 1150 ° C. instead of the Mg-doped GaN layer of the sample described above, the Mg-doped (GaN) _0.8 was added on the n-GaN layer 4.
(SiC) A _0.2 layer 6 was grown for 10 minutes (〜0.3 μm). The obtained sample was heat-treated at 750 ° C. in a nitrogen atmosphere for 30 minutes to activate Mg in the GaN layer.

The p-GaN layer 6 thus obtained was subjected to secondary ion mass spectrometry (SIMS)
When the concentration of Mg in the aN layer was examined, it was about 3 × 10 ¹⁹ cm ⁻³ , which is equivalent to the sample formed by the conventional method. Next, the acceptor concentration and the carrier concentration of this sample were evaluated by capacitance-voltage (CV) measurement and Hall effect measurement. As a result, the acceptor concentration was 1 × 10 ¹⁹ cm ⁻³ and the p-type carrier concentration was 8 ×. It was 10 ¹⁸ cm ^-3 , and the activation rate of Mg as a carrier was about 30%, which was about 30 times higher than the conventional one.

FIG. 2 is a sectional view showing an embodiment in which the present invention is applied to a GaN blue semiconductor laser device. In this embodiment, the present invention is applied to the contact layer for the p-side electrode.

This semiconductor laser device is formed on a sapphire substrate 10. On the sapphire substrate 10,
The n-GaN layer 11 (Si-doped, 3 to 5 × 10 ¹⁸ c) having a hexagonal crystal type (wurtzite type) is formed by MOCVD.
m ⁻³ ), followed by an n-Al _0.2 Ga _0.8 N cladding layer 12 (Si-doped, 5 × 10 ¹⁷ cm ⁻³ , layer thickness 0.1).
5 μm), In _0.15 Ga _0.85 N active layer 13 (andove, 0.1 μm thick), p-Al _0.2 Ga _0.8 N clad layer 14 (Mg doped, 5 × 10 ¹⁷ cm ⁻³ , 0.1 thick)
5 μm) are sequentially grown at 1150 ° C. Ga, Al, I
Trimethylgallium (TM
G), trimethyl aluminum (TMA), trimethyl indium (TMI) and ammonia (NH ₃ ). Silane (SiH ₄ ) and cyclopentadienyl magnesium (Cp ₂ Mg) were used as the n-type and p-type dopants, respectively.

On the p-Al _0.2 Ga _0.8 N cladding layer 14, according to the present invention, the raw material bis-trimethyls11ylmethane used in the embodiment of FIG. 1 is used.
_{[BTMSM (CH 3) 3 -Si} -CH 2 - (CH 3)
₃ ] using Mg-doped (GaN) _0.8 (SiC) _0.2
Contact layer 15 (Mg doped, 5-8 × 10 ¹⁸ c
m ⁻³ , layer thickness 0.1 μm) was continuously grown at 1150 ° C.

Although not particularly shown, the n-GaN layer 1
A GaN buffer layer grown at 550 ° C. at low temperature is provided between the GaN buffer layer 1 and the sapphire substrate 10. Furthermore, G
The p-side electrode 16 is provided on the upper surface of the aN contact layer 15, and the n-side electrode 1 is provided on the upper surface of the n-GaN layer 11 where the n-AlGaN cladding layer 12 is not laminated.
7 are provided.

A cavity mirror was formed on the laser multilayer structure manufactured as described above by cleavage or dry etching, and a blue semiconductor laser device was manufactured.

Next, the oscillation operation of the blue semiconductor laser device having the above configuration will be described. The laser device of this example oscillated continuously at room temperature at a threshold value of 150 mA.
The oscillation wavelength was 395 nm, and the operating voltage was 6V. The operating life of this element is as long as 10,000 hours or more,
Conventionally, since the resistance of the p-type contact is high, deterioration occurs in the contact portion with the electrode, and the problem that the element life is remarkably short has been solved. In this embodiment, in addition to the effect of lowering the resistance, the p-Al _0.2 Ga _0.8 N cladding layer 14 and the Mg
Doped (GaN) _0.8 (SiC) _0.2 Contact layer 15
Since the lattice mismatch difference between the two layers almost disappeared, the interface characteristics between the two layers also improved. As a result, in the device of this example, the yield and the reliability were greatly improved.

FIG. 3 is a sectional view showing an embodiment in which the present invention is applied to a GaN-based semiconductor laser similar to the embodiment shown in FIG. 2. However, not only a contact layer but also a cladding layer (current injection layer) is used. 1 also shows an embodiment to which the present invention is applied.

An AlN buffer layer 21 is grown on the n-SiC substrate 20 at 600 ° C. by MOCVD. N- (GaN) _0.8 (SiC) _0.2 at 1150 ° C.
A layer 22 (Si-doped, 3-5 × 10 ¹⁸ cm ⁻³ ) is formed, followed by n- (Al _0.3 Ga _0.7 N) _0.7 (Si
C) _0.3 cladding layer 23 (Si-doped, 1 × 10 ¹⁸ cm)
^-3 , layer thickness 0.2 μm), In _0.2 Ga _0.8 N active layer 24
(Undoped, 200 angstrom thick).

Next, p- (Al _0.3 Ga
_0.7 N) _0.7 (SiC) _0.3 clad layer 25 (Mg-doped, 1 × 10 ¹⁸ cm ⁻³ , 0.2 μm), and ap-SiC contact layer 26 (Al-doped, 6 × 10
⁽¹⁸ cm ^-3 , layer thickness 0.3 μm).

In this embodiment, trimethyl gallium (TMG), trimethyl aluminum (TMA), trimethyl indium (TMI) and ammonia (NH ₃ ) were used as raw materials for growing Ga, Al, In and N. The n-type and p-type dopants are respectively silane (Si
H ₄ ), cyclopentadienyl magnesium (Cp ₂ M
g) was used. In addition, the SiC according to the embodiment of the present invention
Used for the growth of a compound semiconductor of silicon and nitride semiconductor
The raw material is hexamethyldisilane [H
MDS (CH ₃ ) ₆ Si ₂ ], and p-type dopant material for the p-SiC contact layer is TMA.

In this semiconductor laser device, a current confinement layer 27 made of SiO ₂ having a stripe-shaped opening is provided on the contact layer 26, and a p-side electrode 28 is directly contacted with the contact layer 26 through the opening. Is provided. On the other hand, an n-side electrode 29 is provided on the back side of the n-SiC substrate 20.

A resonator (not shown) mirror was manufactured on the laser multilayer structure having the above structure, and a blue semiconductor laser device was completed.

Next, the oscillation operation of the blue semiconductor laser device having the above configuration will be described. The semiconductor laser device having the double hetero structure according to this embodiment has a threshold value of 70 m.
A continuously oscillated at 60 ° C. at A. The oscillation wavelength is 395nm,
The operating voltage was 5V.

As described above, according to the blue semiconductor laser device of this embodiment, the resistance of the cladding layer and the p-side contact layer can be reduced, the carrier injection efficiency and the current efficiency can be improved, and the stable device can be obtained. The characteristics were obtained, the yield and the life of the device were significantly improved, and a highly reliable blue semiconductor laser device could be manufactured.

FIG. 4 shows a G according to still another embodiment of the present invention.
It is sectional drawing of an aN type semiconductor laser. This embodiment is shown in FIG.
This is a blue semiconductor laser device formed on a sapphire substrate in the same manner as in the above case, and the present invention is applied to the p-side contact layer and the p-type cladding layer as in the case of FIG.

GaN grown at 550 ° C. on the (0001) plane of the sapphire substrate 30 by MOCVD.
N-Ga at 1150 ° C. via a buffer layer (not shown)
N layer 31 (Si Dove, 3~5 × 10 ¹⁸ cm ^-3) is formed, followed by n-Al _0.5 Ga _{0. 5} N cladding layer 32 (S
i-dove, 5 × 10 ¹⁷ cm ⁻³ , layer thickness 0.3 μm), Ga
N light confinement layer 33 (undoped, layer thickness 0.2 μm),
In _0.2 Ga _0.8 N / In _0.05 Ga _0.95 N multiple quantum well active layer 34, GaN optical confinement layer 35 (undoped, layer thickness 0.2 μm), p- (Al _0.5 Ga _0.5 N) _0.7 (S
iC) _0.9 cladding layer 36 (Mg-doped, 5 × 10 ¹⁷ c
m ⁻³ , 0.3 μm). On top of that, p-
(In _0.1 Ga _0.9 N) _0.7 (SiC) _0.3 Contact layer 37 (Mg doped, 1-3 × 10 ¹⁸ cm ⁻³ , 0.1 μm)
m) grow sequentially.

Further, on the upper surface of the contact layer 37, p
A side electrode 38 is provided. On the other hand, the n-GaN layer 31
An n-side electrode 39 is provided on the upper surface portion where the upper n-AlGaN cladding layer 32 is not stacked.

A cavity facet (not shown) was formed on the multilayer film configured as described above, and a blue semiconductor laser device was manufactured. Next, the oscillation operation of the laser device will be described. This laser device continuously oscillated up to 60 ° C. at a threshold value of 72 mA. The oscillation wavelength was 395 nm), and the operating voltage was 6.6 V.

As described above, also in the laser device of this embodiment, since the p-side contact resistance and the resistance of the p-type cladding layer (current injection layer) can be reduced, the life of the device is extended and the reliability is greatly increased. Improved.

The present invention is not limited to the scope of the above-described embodiment.
The present invention can be applied to an electronic device using an N-based light emitting diode (LED) and other nitride-based compound semiconductors, and effects such as a reduction in operating voltage of the element and a prolonged life can be obtained.

As a raw material for growing SiC used in the MOCVD method, bis-trimetilysimethane (bis-trimet
_{hylsi1ylmethane) [BTMSM (CH 3)} 3 -Si-
CH ₂ — (CH ₃ ) ₃ ], hexamethyldisilane (hexam
ethyldisilane) [HMDS (CH ₃ ) ₆ Si ₂ ]
Methyl trichlorosilane (methyltrich1orosilane)
[MTS], silacyc1obutane [S
There are raw materials such as CB], methylsilane, 1.3-disilabutane, etc., in which Si and C are directly bonded. In addition, silane (SiH ₄ ) and propane (C ₃
H ₈ ), disilane (Si ₂ H ₆ ) and acetylene (C ₂ H
₂ ), trichlorosilane (SiHCl ₃ ) and ethylene (C ₂ H ₄ ), hexachlorodisilane (Si ₂ Cl ₆ )
It is also possible to use a combination of Si and C raw materials such as and propane (C ₃ H ₈ ). Further, the crystal can be grown by MOCVD, CVD, MBE (molecular beam epitaxy), LPE (liquid phase growth), or other growth methods.

[0043]

According to the present invention, a nitride semiconductor device,
In particular, in a GaN-based blue semiconductor device, the activation rate of the dopant in the contact layer or the current injection layer has been greatly improved, so that the contact resistance with the electrode and the device resistance can be reduced. In particular, a semiconductor having a wide gap and strong ionic bonding has a poor activation rate of a p-type dopant, a high contact resistance with a p-side electrode, causes device deterioration, and makes laser oscillation difficult in a laser. However, the present invention has solved these problems, and has significantly improved the reliability and yield of the device. Reached the level.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a basic configuration of a semiconductor light emitting device according to the present invention in comparison with a conventional configuration. FIG. 1A is a layer structure according to a conventional technology, and FIG. Is shown.

FIG. 2 is a sectional view showing an embodiment in which the present invention is applied to a GaN-based blue semiconductor laser device.

FIG. 3 is a sectional view showing another embodiment in which the present invention is applied to a GaN-based semiconductor laser.

FIG. 4 is a sectional view of a GaN-based semiconductor laser showing still another embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 sapphire substrate 2 low-temperature GaN buffer layer 3 undoped GaN layer 4 n-GaN layer 5 p-GaN layer 6 p- (GaN) _0.8 (SiC) _0.2 layer 10 sapphire substrate 11 n-GaN layer 12 n-AIGaN cladding layer 13 InGaN Active layer 14 p-AIGaN cladding layer 15 p- (GaN) _0.8 (SiC) _0.2 contact layer 16 p-side electrode 17 n-side electrode 20 n-SiC substrate 21 AlN buffer layer 22 n- (GaN) _0.8 (SiC) _0.2 layer 23 n- (Al _0.3 Ga _0.7 N) _0.7 (SiC) _0.3
Cladding layer 24 undoped In _0.2 Ga _0.8 N active layer 25 p- (Al _0.3 Ga _0.7 N) _0.7 (SiC) _0.3
Cladding layer 26 p-SiC contact layer 27 current confinement layer 28 p-side electrode 29 n-side electrode 30 sapphire substrate 31 n-GaN layer 32 n-Al _0.5 Ga _0.5 N cladding layer 33 GaN light confinement layer 34 In _0.2 Ga _0.8 N / In _0.05 Ga _0.95 N multiple quantum well active layer 35 GaN optical confinement layer 36 p- (Al _0.5 Ga _0.5 N) _0.7 (SiC) _0.9
Cladding layer 37 p- (In _0.1 Ga _0.9 N) _0.7 (SiC) _0.3
Contact layer 38 p-side electrode 39 n-side electrode

Claims (5)

[Claims] An active layer formed on a substrate via a first cladding layer, a contact layer formed on the active layer via a second cladding layer, and formed on the contact layer. A first electrode, and a second electrode provided on the opposite side of the active layer with respect to the first electrode, wherein the contact layer comprises:
1. A nitride-based compound semiconductor light-emitting device comprising a nitride-based compound semiconductor containing Si and C at a ratio of 1: 1. 2. The contact layer or the second cladding layer is a nitride-based compound semiconductor containing at least one element of Ga, Al, In, and B and N in a one-to-one ratio with Si and C.
Wherein a ratio _{of, (Ga a Al b In c} B d N) 1-x (S
iC) _x (where a + b + c + d = 1, 0 ≦ a, b,
2. The nitride-based compound semiconductor light emitting device according to claim 1, comprising a compound represented by c, d.ltoreq.1, 0 <x <1). 3. The method according to claim 1, wherein the first or second cladding layer is made of S
3. The nitride-based compound semiconductor light-emitting device according to claim 1, wherein the light-emitting device is made of a nitride-based compound semiconductor containing i and C at a ratio of 1: 1. 4. An active layer formed on a substrate via a first cladding layer, a contact layer formed on the active layer via a second cladding layer, and formed on the contact layer. A nitride-based compound semiconductor device comprising: a first electrode having a first electrode; and a second electrode provided on the opposite side of the active layer from the first electrode.
A nitride-based compound semiconductor light-emitting device comprising iC. 5. An active layer formed on a substrate via a first cladding layer, a contact layer formed on the active layer via a second cladding layer, and an active layer formed on the contact layer. A first electrode, and a second electrode provided on the opposite side of the active layer with respect to the first electrode, wherein the contact layer comprises:
A nitride-based compound semiconductor light-emitting device comprising a nitride-based compound semiconductor layer and a compound semiconductor layer containing Si and C in a ratio of 1: 1 alternately stacked.