JPH1140892A - Iii nitride semiconductor device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a III nitride semiconductor device to be stabilized in oscillation mode and lessened in operating current by a method, wherein a current constriction structure is formed inside a p-type III nitride layer represented by a formula. SOLUTION: A p<-> high-resistance region 7h which sandwiches strip-like low-resistance p<+> region is formed in a p-type Alx Gay In1-x-y (0<=x, y<=1, 0<=x+y<=1) layer 7 taking advantage of the inactivation phenomenon of acceptor by hydrogen atom. In this structure, carriers (holes) injected through a p-type III nitride N layer electrode are restrained from flowing through the high- resistance p<-> regions 7h but flow only through the stripe-like low-resistance p<+> region. That is, a current constriction structure is formed. Carriers injected through an electrode are trapped in a narrow region adjacent to a stripe inside an active layer. In result, carriers become high in density even at a low current level, an inverted distribution is formed, and a laser oscillation start current (threshold level) can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a group III nitride semiconductor device having a current confinement structure, and more particularly to a light emitting device and a method of manufacturing the same.

[0002]

2. Description of the Related Art Group III nitride semiconductors (AlN, GaN, InN
And their mixed crystals) range from 1.9 eV to 6.2 eV.
Direct-transition semiconductor with a gate gap.
The short-wavelength laser, which is a light source in the visible and ultraviolet
Material to realize laser diodes and light-emitting diodes
Is expected. However, large and high quality bulk single crystals
It is extremely difficult to grow
Fabrication is made of sapphire (Al _TwoO_Three), Spinel (MgAl_TwoO_Four), Charcoal
Printed on a crystalline substrate of silicon carbide (6H-SiC), silicon (Si), etc.
Performed by telo-epitaxial. All are group III nitrides
Substrate and epitaxial lattice
A low-temperature barrier consisting of a low-temperature GaN layer or a low-temperature AlN layer between the films.
High quality epitaxy by interposing a buffer layer
A film is obtained. And silicon (Si) and magnesium
Using n-type (Mg) as a dopant
Mold conductivity control can be realized.

[0003] Short-wavelength laser diodes are realized by laminating group III nitride thin films to form a double heterostructure (hereinafter referred to as a DH structure) or a multiple quantum well structure. In the conventional laser diode, a current confinement structure that limits the current path to only a part of the stripe shape of the active layer for the purpose of reducing operating current, stabilizing the oscillation mode (transverse mode), and limiting the position of the light emitting spot Has been widely adopted. This is not an exception for a laser diode using a group III nitride semiconductor, and is one of the essential technologies for improving characteristics.

FIGS. 4A and 4B are cross-sectional views of a conventional DH laser diode having a current confinement structure using a group III nitride semiconductor. FIG. 4A shows a case of a current confinement structure using electrodes, and FIG. This is the case of a current confinement structure using a mesa structure. AlN buffer layer 2, GaN first layer on insulating substrate 1i
The contact layer _{3, Al X Ga y In 1} -XY first N-cladding layer 4, GaN active layer _{5, Al X Ga y In 1} -XY second N-cladding layer 6 and the GaN of the second The contact layers 7 are sequentially stacked. Then, an epitaxial layer side electrode 8 and a substrate side electrode 9 are respectively formed.

In the case of a current confinement structure using electrodes, an epitaxial side electrode 9 is formed on two insulating layers (silicon oxide layers) Z sandwiching a stripe-shaped gap on the contact layer 7. The stripe-shaped contact portion between the contact layer 7 and the epitaxial side electrode 9 is a current path N. In the active layer, current flows only in the corresponding stripe-shaped region.

In the case of the current confinement structure of the mesa structure, both sides of the contact layer 7 are etched together with the epitaxial side electrode layer to form a mesa structure. The remaining stripe portion is the current path N, and current flows only in the corresponding stripe region in the active layer.

[0007]

However, in these structures, it is difficult to reduce the stripe width to 5 μm or less, and the heat radiation from the epitaxial side of Joule heat during laser oscillation has low heat conduction. Sufficient laser oscillation was difficult to obtain due to the high temperature of the element, which was not sufficient from the electrode via the insulating layer or from the narrow electrode.

An object of the present invention is to provide a group III nitride semiconductor device having a current confinement structure in which an oscillation mode is stabilized and having a low operating current, and a method of manufacturing the same.

[0009]

In order to achieve the above object, in a group III nitride semiconductor device having a current confinement structure, the current confinement structure is a p-type Al _X Ga _y In _1-XYN
(Provided that 0 ≦ x, y ≦ 1, 0 ≦ x + y ≦ 1). The p-type III
Beryllium (Be), magnesium (M
g), at least one of zinc (Zn) and cadmium (Cd) is preferably added as an acceptor.

In the current confinement structure, hydrogen is added to the p-type group III nitride layer from both sides along the surface of the p-type group III nitride layer by two high resistance portions to which hydrogen atoms are further added. It is preferable that a striped portion to which atoms are not added is sandwiched. In the above method for manufacturing a group III nitride semiconductor device, the hydrogen atoms are added by annealing the p-type group III nitride layer in an ammonia (NH ₃ ) atmosphere.

Alternatively, in the above method for manufacturing a group III nitride semiconductor device, the addition of the hydrogen atom may be performed by using the p-type II
This is performed by annealing the group I nitride layer in hydrogen plasma excited by electron cyclotron resonance. It is preferable that the striped portion is formed by performing the annealing while being covered with a striped mask.

The phenomenon in which an acceptor or a donor is inactivated by a hydrogen atom is well known in Si and GaAs. In addition, an MO doped with Mg or Zn as an acceptor is used.
It has been reported that even in a p-type GaN film formed by CVD, H atoms of ammonia (NH ₃ ) used for film formation are incorporated into the film, and the film has a high resistance. Normally, high-resistance films are not suitable for semiconductor devices.

In the present invention, the RF radical beam M
By annealing Mg (or Zn, Be, Cd) doped p-type Al _X Ga _y In _1-XY N layer formed by BE at 600 ° C. to 1000 ° C. in an ammonia atmosphere,
The Al _X Ga _y In _1-XY N layer is changed from low resistance to high resistance. This is because, as in the case of Si, hydrogen atoms in ammonia diffuse into the Al _X Ga _y In _1-XY N layer and combine with the acceptor (Mg or Zn) to form, for example, a Mg-H pair. This is because the acceptor can be inactivated. Further, instead of annealing in an ammonia atmosphere, for example, surface treatment with hydrogen plasma excited by electron cyclotron resonance (hereinafter, referred to as ECR) may be performed to convert hydrogen atoms into Al _X Ga _y In _1-XY N layers. And can cause the inactivation described above.

[0014] Such a hydrogen atom disturbs the acceptor.
Using activation phenomenon, p-type Al_XGa _yIn_1-XYN (however
0 ≤ x, y ≤ 1, 0 ≤ x + y ≤ 1)
High-resistance p- region sandwiching low-resistance p + region
I found that. In this configuration, p-type Al_XGa_yIn
_1-XYThe carriers (holes) injected from the N-layer electrode are
It does not flow through the high-resistance p-region, and has a stripe-like low-resistance p + region.
The current flows only in the region, that is, a current confinement structure is formed.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Carriers injected from electrodes are:
Due to the current confinement structure formed by the inactivation effect of the acceptor by hydrogen, the active layer is confined in a narrow region near the stripe in the active layer. As a result, even at a low current level, the density of carriers becomes high and an inversion distribution is formed, so that a laser oscillation start current (threshold) can be reduced.

On the other hand, in the current dependency characteristic of the laser output, an unstable mode called kink appears when the laser output becomes several mW or more (see curve b in FIG. 3). The instability of the oscillation mode (transverse mode) is an essential problem of the semiconductor laser.
It can be improved by the following. The laser oscillation spot can be limited to a stripe-width region in which carriers in the active layer are confined. Embodiment 1 FIG. 1 shows a DH structure having a current confinement structure according to the present invention.
FIG. 3 is a sectional view of a group I nitride laser diode.

N-type Si (1,1,1) as conductive substrate 1s
A substrate was used. The layer structure is the same as that of the conventional group III nitride laser diode having the DH structure (FIG. 4), but a current confinement structure is formed in the p-type GaN contact layer 7. An RF radical beam MBE method was used for growing each group III nitride layer. N-Si (1,1,1) substrate 1s with carrier density of 1 × 10 ¹⁸ cm ^-3
On top of it, through a low-temperature buffer layer 2 of AlN 2 nm thick,
300 nm thick n-type GaN contact layer 3, 325 nm thick n
The first cladding layer 4 made of type Al _{0. 2} Ga _0.8 N, a thickness of 50 n
Active layer 5 of n-type GaN of m, p-type Al of 325 nm thickness
_A second cladding layer 6 of _0.2 Ga _0.8 N having a thickness of 300 nm;
a second contact layer 7 made of p-type GaN is formed in this order,
DH structure was adopted. n-type GaN contact layer 3, n-type All _0.1
For the Ga _0.8 N cladding layer 4 and the n-type GaN active layer 5, Si (Nd = 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ ) is used as a donor, and p-type
The Al _0.2 Ga _0.8 N cladding layer 6 has Mg (Na
= 1 × 10 ¹⁸ cm ⁻³ ), and Zn (Na = 1 × 10 ¹⁸ cm ⁻³ ) as an acceptor was added to the p-type GaN contact layer 7.

Next, an SiO ₂ film (stripe width 5 μm) is formed on the p-type GaN contact layer 7 by photolithography.
After forming a mask (thickness: 1 μm), in an ammonia atmosphere (pressure
Annealing was performed at 700 ° C. for 7 minutes at 1 atmosphere and a flow rate of 500 sccm. By the above process, two high-resistance portions 7h are formed on the surface of the p-type GaN contact layer 7, and a current confinement structure including a stripe-shaped low-resistance portion having a width of 5 μm sandwiched therebetween is formed. Formed. The longitudinal direction of the stripe is I
It is perpendicular to the cleavage plane (1, -1,0,0) of the group II nitride.

Then, the SiO ₂ film mask is removed, and the Ni / Au epitaxial side electrode 8 and the back surface of the Si substrate are covered with Ti / Ni / Al.
The substrate-side electrodes 9 were formed. The optical resonance surface is Si (1,
The GaN (1, -1,0,0) plane obtained by cleaving the 1,1) plane was used. FIG. 3 shows a D having a current confinement structure according to the present invention.
9 is a graph showing the input pulse current dependency of the optical output of a laser diode having an H structure. Curve a is a laser diode according to the present invention, and curve b is a laser diode having the same layer configuration and no current confinement structure. By forming the current confinement structure in the group III nitride layer, the conventional DH
Laser oscillation at lower current was confirmed as compared with the structure. In addition, kink which is an unstable mode of laser oscillation does not occur. Example 2 In this example, the material of the p-type contact layer in Example 1 was changed from p-type GaN to p-type Al _{0.1 in} order to show that a current confinement structure can be formed even in a group III nitride layer other than GaN.
A constriction structure was fabricated in place of Ga _0.9 N.

However, Mg was added to the p-type contact layer as an acceptor, and its concentration was set to Na = 1 × 10 ¹⁸ cm ⁻³ . The current dependency of the light output of the laser diode having the DH structure is the same as in the first embodiment, and it can be seen that an effective current confinement structure is formed. Example 3 A constriction structure was manufactured by changing the material of the p-type contact layer in Example 1 from p-type GaN to p-type In _0.2 Ga _0.8 N. However, Cd was added as an acceptor to the p-type contact layer, and its concentration was set to Na = 1 × 10 ¹⁸ cm ⁻³ .

The current dependence of the light output of the laser diode having the DH structure is the same as in the first embodiment, and it can be seen that an effective current confinement structure is formed. Example 4 An insulating substrate ((0,0,0,1)) was used instead of the conductive substrate of Example 1.
Plane sapphire substrate).

FIG. 2 is a sectional view of a group III nitride laser diode having a DH structure having a current confinement structure according to the present invention. On the insulating substrate 1i, a DH having the same layer configuration as in the first embodiment is formed.
A group III nitride laser diode having a structure was formed, but hydrogenation for forming a current confinement structure was changed. After a silicon oxide stripe mask was formed on the second contact layer 7, the substrate was treated in a hydrogen plasma excited by electron cyclotron resonance (ECR) to form a p- passivation film. Table 1 shows the conditions of the ECR hydrogen plasma treatment.

[0023]

[Table 1] In the individualization of the element, since the above-mentioned substrate is an insulator, the substrate-side electrode 9 was formed on the first contact layer 2 after the first cladding layer 4 and subsequent portions were removed by etching.

The optical resonance plane is a GaAlN (1,1, -2,0) plane obtained by cleaving the (1, -1,0,0) plane of sapphire. This D
The current dependence of the light output of the laser diode having the H structure is the same as that of the first embodiment, and it can be seen that an effective current confinement structure is formed.

[0025]

According to the present invention, a current confinement structure is provided.
In the group III nitride semiconductor device, the current confinement structure is
p-type Al _X Ga _y In _1-XY N (however, 0 ≤ x, y ≤ 1, 0 ≤
x + y ≦ 1), the current confinement structure can be formed with a narrower current path width than before, the laser oscillation start current is low, and the oscillation mode (transverse mode)
Becomes stable, and the kink of the laser output current characteristic is also improved.

The current confinement structure is formed of beryllium (Be),
Magnesium (Mg), zinc (Zn) or cadmium (C
d) a striped low-resistance portion in which at least one of the elements is added as an acceptor is sandwiched from both sides along the group III nitride layer by a high-resistance portion in which hydrogen atoms are further added to the acceptor. Due to this structure, the resistance of the high-resistance portion is sufficiently high due to the bond between the acceptor and the hydrogen atom, so that the current confinement is reliably performed.

In the above method for manufacturing a group III nitride semiconductor device, the p-type group III nitride layer may be made of ammonia (NH
₃ ) Annealing in atmosphere or in hydrogen plasma excited by electron cyclotron resonance makes it easy to control the diffusion rate of hydrogen atoms, accurately reproduce the size of the high-resistance region, and have a current confining structure. The production yield of semiconductor devices is high.

[Brief description of the drawings]

FIG. 1 shows a DH structure having a current confinement structure according to the present invention.
Sectional view of group III nitride laser diode

FIG. 2 shows a DH structure having a current confinement structure according to the present invention.
Sectional view of group III nitride laser diode

FIG. 3 is a graph showing the input pulse current dependency of the optical output of a DH laser diode having a current confinement structure according to the present invention.

FIG. 4 is a cross-sectional view of a conventional DH laser diode having a current confinement structure using a group III nitride semiconductor, where (a) is a case of a current confinement structure using electrodes;
(B) shows the case of a current confinement structure using a mesa structure

[Explanation of symbols]

 1s Conductive substrate 1i Insulating substrate 2 Buffer layer 3 First contact layer 4 First clad layer 5 Active layer 6 Second clad layer 7 Second contact layer 7h High resistance portion 8 Epitaxial layer side electrode 9 Substrate side Electrode layer N Current path Z Insulation layer

Claims (6)

[Claims] 1. A group III nitride semiconductor device having a current confinement structure, wherein the current confinement structure is a p-type Al _X Ga _y In
_1-XY N (where 0 ≤ x, y ≤ 1, 0 ≤ x + y ≤ 1)
II characterized by being formed in a group III nitride layer
Group I nitride semiconductor device. 2. The p-type group III nitride layer contains at least one element selected from beryllium (Be), magnesium (Mg), zinc (Zn) and cadmium (Cd) as an acceptor. 2. The method according to claim 1, wherein
Group III nitride semiconductor device. 3. The current confinement structure according to claim 1, wherein the p-type group III nitride layer further includes two high-resistance portions to which hydrogen atoms are added, from both sides along the surface of the p-type group III nitride layer. 3. The method according to claim 2, wherein a striped portion to which no hydrogen atom is added is sandwiched.
Group I nitride semiconductor device. 4. The method of manufacturing a group III nitride semiconductor device according to claim 3, wherein the addition of the hydrogen atom is performed by the p-type.
A method for manufacturing a group III nitride semiconductor device, comprising: annealing a group III nitride layer in an ammonia (NH ₃ ) atmosphere. 5. The method of manufacturing a group III nitride semiconductor device according to claim 3, wherein the addition of the hydrogen atom is performed by the p-type.
A method for manufacturing a group III nitride semiconductor light emitting device, characterized in that the group III nitride layer is annealed in hydrogen plasma excited by electron cyclotron resonance. 6. The group III nitride semiconductor light emitting device according to claim 4, wherein said striped portion is formed by performing said annealing while being covered with a striped mask. Manufacturing method.