JP2013179187A - Semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor element that allows high performance of an optical semiconductor element under high temperatures.SOLUTION: A semiconductor device of the present invention includes: a buffer layer formed on a GaAs substrate; a lattice relaxation layer formed on the buffer layer and having an In composition ranging from 5 to 30%; a lower cladding layer formed on the lattice relaxation layer; a quantum well active layer formed on the lower cladding layer; a carrier stopper layer formed on the quantum well active layer and composed of InAlGaAs; and an upper cladding layer composed of InGaP. The lower cladding layer and the upper cladding layer have a refractive index lower than that of the quantum well active layer. The upper cladding layer is formed so that the carrier stopper layer is sandwiched by the quantum well active layer and the upper cladding layer.

Description

  The present invention relates to a semiconductor device that enables high performance of an optical semiconductor device, particularly in a high temperature environment.

  In conventional optical fiber communication using a light source having a wavelength of 1.3 μm to 1.55 μm, an InGaAsP-based laser on an InP substrate, which is easy to produce because of the band gap and lattice constant, has been used. In an InGaAsP-based laser on an InP substrate, usually, a strained quantum well structure is adopted as an active layer in order to improve oscillation characteristics.

  In general, in InGaAsP lasers on InP substrates, it is known that increasing the amount of strain in the quantum well active layer will improve the laser characteristics by improving the differential gain. Invite. Therefore, in consideration of the lattice constant difference with the InP substrate, InGaAsP having a compressive strain of about 1% is used as the quantum well layer and the InGaAsP has a lattice-matched composition with the InP substrate as the barrier layer. Is generally used.

  In such a conventional InGaAsP-based laser on an InP substrate, since the band discontinuity between the quantum well layer on the conduction band side and the barrier layer is small, the optical gain is reduced due to the overflow of electrons under high temperature conditions. It causes an increase in threshold current and a decrease in efficiency. For this reason, the characteristic temperature indicating the temperature dependence of the threshold current is as low as about 50 K, and the use of a temperature regulator has been indispensable.

  Further, an InAlGaAs-based laser that has a band discontinuity larger than that of an InGaAsP-based laser on an InP substrate has been developed. InAlGaAs-based lasers have improved temperature characteristics compared to InGaAsP-based lasers, but their temperature characteristics are still inferior to short-wavelength InGaAs-based lasers on GaAs substrates. Furthermore, in the InAlGaAs-based laser, there is a concern about reliability deterioration due to oxidation inherent to a material containing Al (see, for example, Non-Patent Document 1).

  On the GaAs substrate, 0.78 [mu] m, 0.85 [mu] m, 0.98 [mu] m, and 1.06 [mu] m band lasers having relatively short wavelengths have been put into practical use and show excellent temperature characteristics exceeding a characteristic temperature of 150K. This is due to a large band offset on the conduction band side. In order to obtain light emission at 1.3 μm by the InGaAs / GaAs strained quantum well structure used in the above 0.98 μm and 1.06 μm band lasers, it is necessary to increase the In composition to about 50% (for example, non-patent References 2 and 3).

Tsutomu Munakata, Keizo Takemasa, Masao Kabayashi, Hiroshi Wada, “High-temperature operation of 1.3-μm AIGalnAs / lnP strained multiple quantum well lasers with an AllnAs electron stopper layer”, May 6, 1998, p. 293. H. Fukano, Y. Noguchi, S. Kondo, “1.5 μm InGaAlAs-strained MQW ridge-waveguide laser diodes with hot-carrier injection suppression structure”, ELECTRONICS LETTERS, January 7, 1999, Vol. 35 No. 1. H. Kurakake, T. Uchida, T. Higashi, S, Ogita, M. Kobayashi, “1.3μm high To strained MQW laser with AlGaInAs SCH layers on a hetero-epitaxial InGaAs buffer layer”, September 19, 1994, p. 71-72.

  However, as the In composition increases, the lattice mismatch between the InGaAs quantum well layer and the GaAs substrate increases, resulting in three-dimensional growth and misfit dislocations. Therefore, in an InGaAs laser on a GaAs substrate, a high wavelength band of 1.3 μm or higher Formation of quality quantum wells has been difficult.

  In particular, a buffer layer made of InGaAs or InAlAs is grown on a GaAs substrate, the lattice constant is changed, and in a laser having a wavelength of 1.3 μm or more, which is the communication wavelength band, the lower cladding layer on the GaAs substrate side is flat. In some cases, high InAlGaAs is used, and InGaP is used for the upper clad layer on the opposite side. Usually, the lower cladding layer made of InAlGaAs is doped n-type, and the upper cladding layer made of InGaP is doped p-type. In such a case, since the band gap of the n-type lower cladding layer is larger than the band gap of the p-type upper cladding layer, high-energy electrons injected from the n-type lower cladding layer at high temperatures are generated by the active layer. The rate of non-radiative recombination increases after entering the p-type upper clad layer, causing deterioration of the laser characteristics. Since this phenomenon also occurs in InP substrates and InGaAs-based materials, a solution has been required.

  In the present invention, electrons overflow from the quantum well of the active layer to the cladding layer in a high-temperature environment or in an environment where the internal active layer becomes hot due to self-heating when a large current is applied to the semiconductor laser. It solves the problem of recombination without contributing to light emission and deterioration of characteristics.

  In order to solve the above-described problem, a semiconductor device according to claim 1 of the present invention includes a GaAs substrate, a buffer layer formed on the GaAs substrate, a buffer layer formed on the buffer layer, and the GaAs substrate. A lattice relaxation layer having a lattice constant larger than that of the substrate and having an In composition in the range of 5 to 30%, a lower cladding layer formed on the lattice relaxation layer and doped n-type, and the lower cladding layer A quantum well active layer having a quantum well structure formed thereon, a carrier stopper layer made of p-type doped InAlGaAs formed on the quantum well active layer, and p-type doped InGaP An upper cladding layer, wherein the lower cladding layer and the upper cladding layer have a refractive index lower than that of the quantum well active layer, Rudd layer is characterized by being formed so as to sandwich the carrier stopper layer by the quantum well active layer and the upper cladding layer.

  A semiconductor device according to claim 2 of the present invention is the semiconductor device according to claim 1 of the present invention, wherein the lower clad layer is made of InAlGaAs or InGaP.

  A semiconductor device according to a third aspect of the present invention is the semiconductor device according to the first or second aspect of the present invention, wherein the lower cladding layer and the upper cladding layer are the lower cladding layer and the upper cladding layer, respectively. It has the composition which becomes equal to the lattice constant.

  A semiconductor element according to a fourth aspect of the present invention is the semiconductor element according to any one of the first to third aspects of the present invention, wherein the lower cladding layer and the upper cladding layer are the lower cladding layer and the semiconductor element. The upper clad layer has a composition such that the refractive indexes of the upper clad layers are equal.

  A semiconductor device according to a fifth aspect of the present invention is the semiconductor device according to any one of the first to fourth aspects of the present invention, wherein the buffer layer and the lattice relaxation layer are made of InGaAs or InAlAs. Features.

  A semiconductor element according to a sixth aspect of the present invention is the semiconductor element according to any one of the first to fourth aspects of the present invention, wherein the etching stopper layer formed on the carrier stopper layer and the upper cladding A contact layer formed on the layer; and a buried layer formed on the etching stopper layer so as to sandwich the upper cladding layer formed on the etching stopper layer and the contact layer. Features.

  A semiconductor element according to a seventh aspect of the present invention is the semiconductor element according to the sixth aspect of the present invention, wherein the n-type electrode is formed on the GaAs substrate on the side where the buffer layer is not formed. And a p-type electrode formed on the contact layer.

  A semiconductor element according to an eighth aspect of the present invention is the semiconductor element according to any one of the first to seventh aspects of the present invention, wherein a wavelength having a gain of the quantum well active layer is 1.1 to 1. It is characterized by being 4 μm.

  The semiconductor device according to the present invention is a communication wavelength band semiconductor laser having a buffer layer made of InGaAs or InAlAs having a changed lattice constant on a GaAs substrate, and includes p-type InAlGaAs between a lower cladding layer and an upper cladding layer. A carrier stopper layer. As a result, high-performance semiconductor lasers that can suppress non-light-emitting components that cause electrons to overflow from the lower cladding layer to the upper cladding layer even in a high-temperature environment and do not require a temperature regulator with little change in characteristics. Can be realized.

It is a figure which shows the layer structure of the semiconductor element which concerns on this invention. It is a figure which shows the temperature dependence of the threshold current of a semiconductor laser.

  As a result of conducting numerous experimental studies to solve the above problems, the present inventors have grown a buffer layer and a lattice relaxation layer on a substrate using a metal organic vapor phase epitaxy method (MOVPE method). When a carrier stopper layer is introduced between the quantum well active layer and the upper clad layer on the lower clad layer when the lower clad layer and the upper clad layer are grown thereon, the temperature dependence of the threshold current of the semiconductor laser It has been found that the properties are remarkably reduced, that is, the temperature characteristics are remarkably improved, and the present invention has been achieved based on this finding.

FIG. 1 shows a layer structure of a semiconductor device 100 according to the present invention. FIG. 1 shows an n-type electrode 101, a GaAs substrate 102, a buffer layer 103 made of n _- type In _x Ga _1-x As, a lattice relaxation layer 104 made of n-type In _y Ga _1-y As, a lower cladding layer 105, The quantum well active layer 106, the carrier stopper layer 107, and the etching stopper layer 108 are sequentially stacked, the buried layer 109 and the upper cladding layer 110 are formed on the etching stopper layer 108, and the contact layer 111 is formed on the upper cladding layer 110. A semiconductor laser 100 in which a p-type electrode 112 is formed on a buried layer 109 and a contact layer 111 is shown. The buried layer 109 is formed on the etching stopper layer 108 so as to sandwich the upper cladding layer 110 and the contact layer 111.

  Hereinafter, the configuration and manufacturing method of the semiconductor element 100 according to the present invention will be exemplified. The growth of each layer at the time of manufacturing the semiconductor device 100 according to the present invention was performed using a metal organic chemical vapor deposition method (MOVPE method). Here, the numerical values and the like described below are exemplifications and are not intended to limit the present invention.

First, a buffer made of n-type In _x Ga _1-x As doped with 1 × 10 ¹⁸ (cm ⁻³ ) Si on a 100 nm-thick GaAs substrate 102 doped with Si 5 × 10 ¹⁷ (cm ⁻³ ). Layer 103 is grown to 1600 nm. The In composition of the buffer layer 103 made of n-type In _x Ga _1-x As can be 12% (x = 0.12).

Next, the lattice relaxation layer 104 made of n-type In _y Ga _1-y As doped with 5 × 10 ¹⁷ (cm ⁻³ ) of Si is grown on the buffer layer 103 by 300 nm. The lattice relaxation layer 104 has a lattice constant larger than that of the GaAs substrate 102 and is relaxed. The In composition of the lattice relaxation layer 104 made of n-type In _y Ga _1-y As can be 10% (y = 0.1). In order to realize light emission in the optical fiber communication wavelength band, the In composition of the lattice relaxation layer 104 is 5% to 30% (y = 0.05 to 0.30) from the relationship between the strain of the quantum well and the lattice constant. It may be in the range. Since the lattice relaxation layer 104 having such an In composition is substantially lattice-relaxed, the layers from the GaAs substrate 102 to the lattice relaxation layer 104 can be regarded as a pseudo InGaAs substrate.

Next, a lower cladding layer 105 made of n-type InAlGaAs having a thickness of 1.5 μm doped with Si of 1 × 10 ¹⁸ (cm ⁻³ ) is grown on the lattice relaxation layer 104. Next, the quantum well active layer 106 having a strained quantum well structure in which an In _0.1 Ga _0.9 As barrier layer is disposed on both sides of the compression strained quantum well layer on the lower cladding layer 105 and having a gain of 1.3 μm band, for example. To grow. The wavelength having the gain of the quantum well active layer 106 can be 1.1 to 1.4 μm.

  Next, a carrier stopper layer 107 made of p-type InAlGaAs is grown on the quantum well active layer 106 by 30 nm, and an etching stopper layer 108 made of p-type InGaAs is further grown by 30 nm. A double hetero laser structure with a quantum well active layer 106 sandwiched therebetween is fabricated.

Next, an upper cladding layer 110 made of p-type InGaP is grown on the etching stopper layer 108 by 1500 nm. The lower cladding layer 105 and the upper cladding layer 110 have a refractive index lower than that of the quantum well active layer 106. Since the upper clad layer 110 is mesa-processed, InGaP which is difficult to oxidize is suitable. Next, a contact layer 111 made of In _0.1 Ga _0.9 As doped with 2 × 10 ¹⁹ (cm ⁻³ ) p-type is grown on the upper clad layer 110 to a thickness of 100 nm.

Next, a SiO ₂ layer is deposited on the contact layer 111 by sputtering, and a striped mask is formed on the SiO ₂ layer by photolithography. Next, a mesa stripe having a width of 1.7 μm is formed by dry etching, and both sides of the upper cladding layer 110 and the contact layer 111 formed in a mesa shape are embedded with SiO ₂ and polyimide to thereby form the upper cladding layer 110 and the contact. A buried layer 109 is formed so as to sandwich the layer 111. Next, after polishing the GaAs substrate 102, the n-type electrode 101 is formed on the GaAs substrate 102 on the side where the buffer layer 103 is not formed, the p-type electrode 112 is formed on the contact layer 111, and the ridge laser is formed. Process. On the light emitting side, the cleavage plane remains as it is, and on the opposite surface, a multilayer film reflecting mirror capable of obtaining a high reflectivity of about 90% is laminated. The produced laser had an oscillation wavelength of 1.3 μm.

  As described above, in the semiconductor device 100 according to the present invention, the carrier stopper layer 107 made of p-type InAlGaAs having a large band gap is formed between the quantum well active layer 106 and the upper cladding layer 110. Accordingly, it is possible to manufacture a high-performance semiconductor laser that suppresses leakage of high-energy electrons to the upper cladding layer 110 in a high-temperature environment or high-current operation in which self-heating is significant and does not require a temperature regulator. It becomes possible.

  FIG. 2 shows the temperature dependence of the threshold current of the semiconductor laser. In FIG. 2, the temperature dependence of the threshold current of the semiconductor element of the present invention having a cavity length of 1200 microns and having a carrier stopper layer made of p-type InAlGaAs and the prior art semiconductor element having no carrier stopper layer is shown on the same graph. Plot to As shown in FIG. 2, the semiconductor element of the present invention having a carrier stopper layer suppresses an increase in threshold current when the temperature rises as compared with a conventional semiconductor element without a carrier stopper layer. The effect was clearly confirmed.

Here, in the semiconductor device 100 according to the present invention, n-type In _x Ga _1-x As is used as the buffer layer 103 and n-type In _y Ga _1-y As is used as the lattice relaxation layer 104. It is also possible to use n-type In _x Al _1-x As as the layer 103 and n-type In _y Al _1-y As as the lattice relaxation layer 104 (In composition is the same as above). In the semiconductor element 100 according to the present invention, n-type InAlGaAs is used as the lower cladding layer 105, but n-type InGaP can also be used.

Further, the lower cladding layer 105 and the upper cladding layer 110 are preferably configured so that the lattice constants of the lower cladding layer 105 and the upper cladding layer 110 are equal. Furthermore, it is preferable that the lower clad layer 105 and the upper clad layer 110 have compositions such that the refractive indexes of the lower clad layer 105 and the upper clad layer 110 are equal. For example, the lower clad layer 105 is composed of In _0.09 Al _0.61 Ga _0.3 As and the upper clad layer 110 is composed of In _0.58 Ga _0.42 P. Can be configured.

DESCRIPTION OF SYMBOLS 100 Semiconductor element 101 N-type electrode 102 GaAs substrate 103 Buffer layer 104 Lattice relaxation layer 105 Lower clad layer 106 Quantum well active layer 107 Carrier stopper layer 108 Etching stopper layer 109 Embedded layer 110 Upper clad layer 111 Contact layer 112 P-type electrode

Claims (8)

A GaAs substrate;
A buffer layer formed on the GaAs substrate;
A lattice relaxation layer formed on the buffer layer, having a lattice constant larger than that of the GaAs substrate and having an In composition in the range of 5 to 30%;
A lower cladding layer formed on the lattice relaxation layer and doped n-type;
A quantum well active layer having a quantum well structure formed on the lower cladding layer;
A carrier stopper layer formed on the quantum well active layer and made of p-type doped InAlGaAs;
an upper cladding layer made of p-type doped InGaP,
The lower cladding layer and the upper cladding layer have a refractive index lower than that of the quantum well active layer, and the upper cladding layer includes the carrier stopper layer formed by the quantum well active layer and the upper cladding layer. A semiconductor element characterized by being sandwiched.   The semiconductor device according to claim 1, wherein the lower cladding layer is made of InAlGaAs or InGaP.   3. The semiconductor device according to claim 1, wherein the lower cladding layer and the upper cladding layer have a composition such that lattice constants of the lower cladding layer and the upper cladding layer are equal to each other.   4. The semiconductor device according to claim 1, wherein the lower clad layer and the upper clad layer have compositions such that refractive indexes of the lower clad layer and the upper clad layer are equal. 5.   The semiconductor element according to claim 1, wherein the buffer layer and the lattice relaxation layer are made of InGaAs or InAlAs. An etching stopper layer formed on the carrier stopper layer;
A contact layer formed on the upper cladding layer;
6. The semiconductor device according to claim 1, further comprising: a buried layer formed on the etching stopper layer so as to sandwich the upper clad layer formed on the etching stopper layer and the contact layer. A semiconductor device according to claim 1. An n-type electrode formed on the GaAs substrate on the side where the buffer layer is not formed;
The semiconductor device according to claim 6, further comprising a p-type electrode formed on the contact layer.   8. The semiconductor element according to claim 1, wherein the wavelength having the gain of the quantum well active layer is 1.1 to 1.4 [mu] m.

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