JPH09129981A - Semiconductor light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical semiconductor device comprising an InP substrate, which has a low oscillation threshold voltage. SOLUTION: A p-contact layer 105 is formed on a p-clad layer 104. The p-contact layer 105 comprises strained superlattice layers of ten short periods of N-doped p-type ZnTe/N-doped p-type ZnSe (ZnTe: 0.3nm/ZnSe: 0.3nm, ZnTe: 0.4nm/ZnSe: 0.4nm, ZnTe: 0.5nm/ZnSe: 0.5nm, ZnTe: 0.6nm/ZnSe: 0.6nm,..., and ZnTe: 1.2nm/ZnSe: 1.2nm). The contact layer has a high doping concentration and good crystallization. In addition, it can effectively have a low barrier to holes by gradually increasing its thickness, so that the device can operate at a low voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device using a II-VI group compound semiconductor, and more particularly to a light emitting diode and a semiconductor laser.

[0002]

2. Description of the Related Art Wide-gap II-VI group compound semiconductors have been widely studied as materials for green-blue semiconductor lasers and light-emitting diodes, but most of them have been manufactured using a GaAs substrate and have room temperature. CW oscillation in literature ⁽¹⁾ (Electronics Letters (Electronics
Letters), Vol. 29, No. 16, 1993, No. 148
8 to 1489), Reference ⁽²⁾ (Electronics Letters, Vol. 29, No. 25,
1993, pp. 2192-2193), and reference ^(3).
(Japanese Journal of Applied Physic
s), Vol. 33, No. 7A, 1994, 938-940.
Page) etc.

On the other hand, Japanese Unexamined Patent Publication No. 5-21892 discloses that
A clad layer and an active layer are epitaxially grown on an InP substrate for the purpose of constructing a semiconductor laser capable of emitting short wavelength, for example, blue, violet, and ultraviolet rays using an InP substrate. -VI
A semiconductor laser made of a group compound semiconductor has been proposed (that is, in the publication, a IIa-VI group compound semiconductor made of group IIa Mg has a relatively large lattice constant, and an InP substrate having a relatively large lattice constant is used. Due to Mg, the IIa-VI group compound has a relatively large band gap, which is advantageous for achieving lattice matching.
It is described that a semiconductor laser capable of emitting a short wavelength, which is well lattice-matched to an InP substrate and is excellent in stability of crystal characteristics and the like, is realized by a II-VI group compound semiconductor specified by a group-VI mixed crystal. ).

In the semiconductor laser described in the above publication, the p-type cladding layer (second layer formed on the active layer
The structure is such that the electrode is directly vapor-deposited on the clad layer).

[0005]

In such a conventional structure, ZnCd used as a p-type clad layer is used.
Se and ZnMgCdSe do not have a p-doping concentration enough to obtain ohmic contact.

In a material system containing Te such as ZnSeTe and ZnMgSeTe, it is easy to obtain a high concentration of p-doping, but it is difficult to do n-doping and Te.
Since the compounds are likely to cause clustering, a film with good crystallinity has not been obtained so far.

The present invention has been made in view of the above problems, and provides a semiconductor light emitting device having a p-type contact layer structure having a low resistance and good crystallinity because of lattice matching with a substrate. The purpose is to provide.

[0008]

In order to achieve the above object, the present invention comprises an InP substrate on which at least a cladding layer made of a II-VI group compound semiconductor lattice-matched to the substrate and an active layer are epitaxially grown. In the semiconductor light emitting device, a ZnSe layer and a ZnTe layer doped with a group V element are alternately stacked as a p-type contact layer,
Each layer has the same layer thickness, the average lattice constant matches the lattice constant of the substrate, and the layer thickness is 1
Provided is a semiconductor light emitting device having a short-period strained superlattice structure which starts from a layer thickness of about an atomic layer and is gradually thickened below a critical film thickness at which lattice relaxation occurs.

In the present invention, the cladding layer is Z
containing one of nCdSe and ZnMgCdSe,
The active layer contains one of ZnCdSe and ZnMgCdSe.

The present invention is characterized in that the group V element contains at least one selected from the group consisting of nitrogen, arsenic, phosphorus and lithium.

[0011]

In the p-type contact layer of the present invention, ZnS
Since the e layer can be doped with an acceptor concentration of 1 × 10 ¹⁸ cm ⁻³ and the ZnTe layer with a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more, the outermost ZnTe layer can be in ohmic contact with the metal electrode. .

Further, in the superlattice structure of the present invention, the barrier against holes is effectively reduced between the outermost ZnTe layer and the cladding layer, so that the current easily flows.

Further, (ZnSe) _0.5 / (ZnTe)
_Since the average lattice constant of the _0.5 superlattice structure is equal to that of the InP substrate, the crystallinity is good.

From the above, in the present invention,
Since the p-type contact layer having a low resistance is formed, the driving voltage of the semiconductor light emitting element is lowered.

[0015]

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

FIG. 1 is a diagram schematically showing a cross section of a green-blue semiconductor laser for explaining the first embodiment of the present invention.

In this embodiment, the Sn-doped InP (100) plane is used as the substrate 100.

First, ZnCdSe is formed on the substrate 100.
The buffer layer 101 is stacked to a thickness of 0.1 μm.

Further, chlorine (Cl) -doped n-type ZnMgCdSe having a layer thickness of 1.5 μm that lattice-matches the InP substrate.
First cladding layer 10 composed of (5 × 10 ¹⁷ cm ⁻³ ).
2. An active layer 103 made of an undoped ZnCdSe layer having a layer thickness of 10 nm and a second clad layer 104 made of nitrogen (N) -doped p-type ZnMgCdSe (1 × 10 ¹⁷ cm ⁻³ ) having a layer thickness of 1.5 μm are laminated in this order. Then, on the second cladding layer 104, an N-doped p-type ZnTe / N-doped p-type ZnSe superlattice layer (ZnSe: 0.3 nm / ZnT
e: 0.3 nm, ZnSe: 0.4 nm / ZnTe:
0.4 nm, ZnSe: 0.5 nm / ZnTe: 0.5
nm, ZnSe: 0.6 nm / ZnTe: 0.6 nm,
..., ZnSe: 1.2 nm / ZnTe: 1.2 nm, 1
The contact layer 105 is formed of 0 cycles.

Then, an insulating film 106 such as a silicon nitride film is deposited on the contact layer 105, a window is opened in a stripe shape, and a first electrode 107 which makes ohmic contact with the p-type contact layer 105 is formed through this window. did.

Instead of forming the insulating film 106 and the electrode 107 in the illustrated state, the p-type contact layer 105 is patterned in a stripe shape, and an insulating film is formed on both sides of the p-type contact layer 105 to fill the p-type contact layer. You may make it form a 1st electrode on it.

Further, a second electrode 108 which makes ohmic contact with the InP substrate 100 is formed on the back surface of the substrate.

When a voltage was applied in the forward direction between the electrodes 105 and 108 in the semiconductor laser thus constructed, room temperature continuous oscillation was performed at 570 nm.

At this time, the oscillation threshold voltage _Vth is 3-4V.
was gotten.

FIG. 2 is a diagram schematically showing a cross section of a green-blue semiconductor laser according to the second embodiment of the present invention.

In this embodiment, a Sn-doped InP (100) plane is used as the substrate 200.

On this substrate 200, a ZnCdSe buffer layer 201 is first laminated to a thickness of 0.1 μm.

Furthermore, chlorine (Cl) -doped n-type ZnMgCd with a layer thickness of 1.5 μm that lattice-matches the InP substrate 200.
First clad layer 2 made of Se (5 × 10 ¹⁷ cm ⁻³ ).
02, undoped ZnMgCd having a layer thickness of 10 nm and a bandgap smaller than that of the first cladding layer 202.
Active layer 203 made of Se layer, second clad layer made of nitrogen (N) -doped p-type ZnMgCdSe (1 × 10 ¹⁷ cm ⁻³ ) having a thickness of 1.5 μm and the same bandgap as the first clad layer. 204 are laminated in this order, and N-doped p-type ZnTe / N is further formed on the second cladding layer 204.
Doped p-type ZnSe superlattice layer (ZnSe: 0.3 nm /
ZnTe: 0.3 nm, ZnSe: 0.4 nm / ZnT
e: 0.4 nm, ZnSe: 0.5 nm / ZnTe:
0.5 nm, ZnSe: 0.6 nm / ZnTe: 0.6
nm, ..., ZnSe: 1.2 nm / ZnTe: 1.2 n
m, 10 cycles) is formed.

Then, an insulating film 206 such as a silicon nitride film is deposited on the contact layer 205, a window is opened in a stripe shape, and a first electrode 207 which makes ohmic contact with the p-type contact layer 205 through the window is formed. did.

Instead of forming the insulating film 206 and the electrode 207 in the illustrated state, the p-type contact layer 205 is patterned in a stripe shape, and insulating films are formed on both sides of the p-type contact layer 205 to fill the p-type contact layer. You may make it form a 1st electrode on it.

Further, a second electrode 208 which is in ohmic contact with the InP substrate 200 is formed on the back surface of the substrate.

When a voltage was applied in the forward direction between the electrodes 205 and 208 in the semiconductor laser thus constructed, room temperature continuous oscillation was performed at a wavelength of 520 nm.

At this time, the oscillation threshold voltage _Vth is also 3-4V.
was gotten. In the present embodiment, the emission wavelength of the semiconductor laser can be changed depending on the composition of Mg in the active layer, and can take an arbitrary value from about 600 nm to about 400 nm.

Although a single quantum well structure is used as the active layer in the above embodiment, the invention is not limited to this, and a multiple quantum well (MQW) may be used.

Also, the laser structure is not limited to the structure described in the above embodiment, and for example, the active layer 10 is used.
3 or 203, various structures can be adopted, such as a structure in which a high-resistance undoped ZnS or the like is formed so as to form a current confinement region on both sides so as to form a stripe-shaped resonator portion in the central portion. .

[0036]

As described above, according to the present invention,
Since the resistance in the p-type electrode can be reduced, a low oscillation threshold voltage can be obtained.

[Brief description of the drawings]

FIG. 1 is a view for explaining a first embodiment of the present invention, II
FIG. 4 is a diagram schematically showing a cross section of a green-blue semiconductor laser structure formed of a group IV compound semiconductor growth layer.

FIG. 2 is a view for explaining a second embodiment of the present invention, II
FIG. 4 is a diagram schematically showing a cross section of a green-blue semiconductor laser structure formed of a group IV compound semiconductor growth layer.

[Explanation of symbols]

 100 Sn-doped InP (100) substrate 101 Cl-doped ZnCdSe buffer layer 102 Cl-doped ZnMgCdSe n cladding layer 103 Undoped ZnCdSe active layer 104 N-doped ZnMgCdSe p-cladding layer 105 p-type ZnSe / ZnTe contact layer 106 Insulating film 107 p-electrode 108 n-electrode 200 Sn-doped InP (100) substrate 201 Cl-doped ZnCdSe buffer layer 202 Cl-doped ZnMgCdSe n cladding layer 203 Undoped ZnMgCdSe active layer 204 N-doped ZnMgCdSe p-cladding layer 205 p-type ZnSe / ZnTe contact layer 206 Insulating film 207 p-electrode 208 n-electrode

Claims (4)

[Claims] 1. A semiconductor light emitting device comprising an InP substrate, at least a clad layer made of a II-VI group compound semiconductor lattice-matched to the substrate, and an active layer epitaxially grown, wherein a group V element is used as a p-type contact layer. Doped Z
nSe layers and ZnTe layers are alternately laminated, each layer has the same layer thickness, the average lattice constant matches the lattice constant of the substrate, and the layer thickness is about one atomic layer. A semiconductor light emitting device having a short period strained superlattice structure which starts from a thickness and is gradually thickened below a critical film thickness at which lattice relaxation occurs. 2. The clad layer is ZnCdSe or Zn
The semiconductor light emitting device according to claim 1, further comprising MgCdSe, wherein the active layer comprises ZnCdSe or ZnMgCdSe. 3. The semiconductor light emitting device according to claim 2, wherein the group V element includes at least one selected from the group consisting of nitrogen, arsenic, phosphorus, and lithium. 4. A semiconductor light emitting device including an n-clad layer, an active layer, and a p-clad layer on an InP substrate or a substrate lattice-matched to InP, wherein the cladding layer and the active layer are lattice-matched to the substrate.
It is made of a II-VI group compound semiconductor containing nCdSe or ZnMgCdSe, and Z is formed by doping a group V element on the p-clad layer.
A semiconductor light-emitting device comprising a contact layer formed by stacking a superlattice made of nSe / ZnTe so that its average lattice constant matches the substrate, and an electrode in ohmic contact with the contact layer. element.