JP2007288068A - Epitaxial wafer for light emission and light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epitaxial wafer for light emission having a p-type contact layer whose contact resistance with an electrode is small, and whose thermal treatment is made unnecessary, and to provide a light emitting element. <P>SOLUTION: An epitaxial wafer for light emission is provided with a light emitter configured of an n-type AlGaAs clad layer 3, an active layer 4, and a p-type AlGaAs clad layer 5 on an n-type GaAs substrate 1; and a p-type InGaAs contact layer 6 is formed as an electrode formation layer on the p-type AlGaAs clad layer 5. The light emitting element is manufactured by using the epitaxial wafer for the light emitting element, and an electrode 7 is formed at the n-type GaAs substrate 1 side, and a non-alloy system p-electrode 8 is formed at the p-type InGaAs contact layer 6 side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an epitaxial wafer and a light emitting element for light emitting elements such as LD (Laser Diode) and LED (Light Emitted Diode).

  Semiconductor laser diodes (LDs) using III / V group compound semiconductor crystals such as AlGaAs and AlGaInP are widely used as light sources for reading and writing in optical disc systems such as digital versatile discs (DVD) and compact discs (CD). It is used. Light emitting diodes (LEDs) are used in various applications such as displays, remote controllers, sensors, and in-vehicle lamps.

  One method for growing compound semiconductor crystals is metal organic vapor phase epitaxy (hereinafter referred to as MOVPE method). In the MOVPE method, a group III organometallic source gas and a group V source gas are introduced into a growth reactor as a mixed gas with a high purity hydrogen carrier gas, and the source material is pyrolyzed in the vicinity of the substrate heated in the growth reactor. A compound semiconductor crystal is epitaxially grown on the substrate.

  As shown in FIG. 4, the conventional AlGaAs laser diode epitaxial wafer includes an n-type buffer layer 42, an n-type AlGaAs cladding layer 43, an active layer 44, and a p-type AlGaAs cladding layer on an n-type GaAs substrate 41. Some have a structure in which 45 and p-type GaAs contact layers 46 are sequentially laminated. The n-type AlGaAs cladding layer 43, the active layer 44, and the p-type AlGaAs cladding layer 45 form a light emitting portion having a double hetero structure. The light emitted from the active layer 44 repeats total reflection at the interface between the active layer 44 and the AlGaAs cladding layers 43 and 45, is guided through the active layer 44, and is emitted to the outside from the crystal end face.

  In the laser diode, an n-electrode 47 is formed on the n-type GaAs substrate 41 and a p-electrode 48 is formed on the p-type AlGaAs cladding layer 45 in order to inject a forward current into the light emitting portion of the laser diode epitaxial wafer. At this time, in order to realize ohmic contact between the p-electrode 48 and the semiconductor, the p-type GaAs contact layer 46 doped with p-type impurities at a high concentration between the p-type AlGaAs cladding layer 45 and the p-electrode 48. Is interposed. In the p-type layer, zinc (Zn) and magnesium (Mg) are used as impurities, and in the n-type layer, silicon (Si) is used as impurities.

  However, in the p-type GaAs contact layer 46, it is difficult to obtain good ohmic characteristics. That is, the contact resistance between the p-electrode 48 and the p-type GaAs contact layer 46 is large, and the voltage-current characteristics of the laser diode may become abnormal.

  Therefore, as a method for reducing the contact resistance between the p-electrode 48 and the p-type GaAs contact layer 46, the metal material of the p-electrode 48 is selected, and further, the heat treatment (alloy) process after forming the p-electrode is optimized. There are also proposed methods for reducing the width of the surface depletion layer by increasing the doping concentration of the p-type GaAs contact layer 46.

In the technical field of heterobipolar transistors (HBT), it is known that an ohmic electrode formed on a p-type InGaAs base layer is a Pd / Zn / Pt / Au layer (see, for example, Patent Document 1). .
JP-A-6-310706

  However, it has been difficult to stably obtain a low resistance value by the above-described method for selecting the p-electrode material and optimizing the heat treatment (alloy) process after forming the p-electrode. In addition, limiting the heat treatment conditions necessary for ohmic contact has also been an obstacle. In other words, if the heat treatment proceeds, the contact resistance increases due to alloying between the electrode metal and the semiconductor, or the impurity concentration distribution in the epitaxial growth layer changes due to thermal diffusion of dopant impurities in the semiconductor. As a result, desired LD characteristics could not be obtained.

Further, in the method of increasing the doping concentration into the p-type GaAs contact layer 46 and reducing the surface depletion layer width, even if the GaAs contact layer 46 is doped with Zn at a high concentration and epitaxially grown, Zn is active at a certain concentration or more. Therefore, the obtained carrier concentration is at most 5 × 10 ¹⁸ cm ⁻³ . Further, when a p-electrode 48 is formed on the heavily doped GaAs contact layer 46 and activation heat treatment is performed, Zn in the p-type AlGaAs cladding layer 45 diffuses into the active layer 44 to obtain desired light emission characteristics. There was also a problem that it was not possible.

  The present invention has been made to solve the above-described problems, and provides an epitaxial wafer and a light-emitting element for a light-emitting element having a p-type contact layer that has a small contact resistance with an electrode and can eliminate heat treatment. is there.

  According to a first aspect of the present invention, an n-type AlGaAs cladding layer, an active layer, and a p-type AlGaAs cladding layer are provided on an n-type GaAs substrate, and an electrode forming layer is formed on the p-type AlGaAs cladding layer. , An epitaxial wafer for a light emitting device in which a p-type InGaAs contact layer is formed.

  A second invention is an epitaxial wafer for light-emitting elements according to the first invention, wherein the p-type InGaAs contact layer has a thickness of 10 nm to 0.2 μm.

  A third invention is an epitaxial wafer for light-emitting elements according to the first or second invention, wherein the p-type dopant of the p-type InGaAs contact layer is Zn or Mg.

  A fourth invention is produced using the epitaxial wafer for a light emitting device according to any one of the first to third inventions, wherein an n electrode is provided on the n-type GaAs substrate side and a non-alloy system is provided on the p-type InGaAs contact layer side. The p-electrode is a light emitting element.

  In the epitaxial wafer for light emitting device of the present invention and the light emitting device using the same, by adopting InGaAs for the p-type contact layer as the electrode forming layer, the contact resistance with the electrode can be reduced and the ohmic characteristics can be obtained. Cheap. In the light emitting device of the present invention, it is possible to eliminate the heat treatment for activating the p electrode, and it is possible to prevent and reduce the diffusion of impurities into the active layer causing the deterioration of the light emission characteristics. Luminous properties can be obtained.

Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the epitaxial wafer for laser diodes of this embodiment has an n-type GaAs buffer layer 2 and an n-type Al _y Ga _1-y As cladding layer 3 (0 <y < 0.6), an active layer 4 having a quantum well structure, a p-type Al _y Ga _1-y As cladding layer 5 (0 <y <0.6), and a p-type InGaAs contact layer 6 are sequentially epitaxially grown. . Zinc (Zn) or magnesium (Mg) is used as the p-type impurity, and silicon (Si) is used as the n-type impurity.

  In the production of the laser diode, as shown in FIG. 1, n made of gold (Au) / gold-germanium (AuGe) / gold (Au) is formed on the back surface of the n-type GaAs substrate 1 with respect to the epitaxial wafer. In addition to forming the electrode 7, a non-alloy p electrode 8 made of titanium (Ti) / platinum (Pt) / gold (Au) was formed on the p-type InGaAs contact layer 6. After forming the electrodes, a chip cut from the wafer was mounted on a stem to produce a laser diode.

  In the present embodiment, the p-type contact layer that is an electrode forming layer for forming the p-electrode 8 is changed from the conventional p-type GaAs contact layer to the p-type InGaAs contact layer 6. For this reason, the Fermi level pinning effect (surface pinning) due to the high-density surface level, which is a problem in GaAs, is eliminated, and the Schottky barrier height is lowered, so that the ohmic characteristics are improved. Furthermore, since no heat treatment for activation is required after electrode formation, impurity diffusion into the active layer 4 causing the deterioration of the light emission characteristics is eliminated, and the light emission characteristics are improved.

The thickness of the p-type InGaAs contact layer 6 is preferably 10 nm to 0.2 μm. The reason is that when the thickness of the p-type InGaAs contact layer 6 exceeds 0.2 μm, a phenomenon in which the contact resistance increases is observed. It is estimated that the reason why the contact resistance increases is due to dislocations generated in the p-type InGaAs contact layer 6 due to lattice mismatch with the p-type Al _y Ga _1-y As cladding layer 5. In addition, if the minimum thickness of the p-type InGaAs contact layer 6 is 10 nm, a sufficiently low resistance can be obtained.

  In the above embodiment, an AlGaAs laser diode epitaxial wafer and a laser diode using the AlGaAs laser diode have been described. However, the present invention can also be applied to an AlGaAs light emitting diode epitaxial wafer and a light emitting diode. The present invention is applicable not only to AlGaAs-based but also to AlGaInP-based epitaxial wafers and light-emitting elements.

Next, specific examples of the present invention will be described.
The epitaxial wafer for laser diode (LD) and the laser diode (LD) of this example have the same structure as that of the above embodiment shown in FIG.

The epitaxial growth of the LD epitaxial wafer was performed by the MOVPE method. In the epitaxial growth by the MOVPE method, TMG (trimethylgallium) was used as a Ga raw material, TMA (trimethylaluminum) was used as an Al raw material, and AsH ₃ (arsine) was used as an As raw material. As dopants, Si ₂ H ₆ (disilane) was used as a raw material for Si as an n-type impurity, and DEZ (diethyl zinc) was used as a raw material for Zn as a p-type impurity.

An AlGaAs-based LD epitaxial wafer has a 200 nm Si-doped GaAs (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) n-type GaAs buffer layer 2 on a conductive n-type GaAs substrate 1 and a 2000 nm Si An n-type AlGaAs cladding layer 3 made of doped Al _0.6 Ga _0.4 As (carrier concentration 8.5 × 10 ¹⁷ cm ⁻³ ) was grown, and an active layer 4 was grown thereon. The active layer 4 has a quantum well structure in which GaAs is a well layer and Al _0.6 Ga _0.4 As is a barrier layer, and no impurity is added. A p-type AlGaAs cladding layer 5 made of Zn-doped Al _0.6 Ga _0.4 As (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) of 2000 nm was grown thereon. A p-type InGaAs contact layer 6 made of Zn-doped In _0.5 Ga _0.5 As (carrier concentration 1 × 10 ¹⁹ cm ⁻³ ) of 50 nm was grown on the uppermost layer. Although not shown in FIG. 1, between the p-type AlGaAs cladding layer 5 and the p-type InGaAs contact layer 6, the p-type In _{0 → 0.5} Ga _{1 → 0 in which the} In composition changes to a gradient type. _{.5 The} lattice mismatch was relaxed by interposing an As layer. The thickness of the inclined p-type In _{0 → 0.5} Ga _{1 → 0.5} As layer was 50 nm.

  Next, an electrode forming process for forming an n-electrode 7 on the n-type GaAs substrate 1 and a p-electrode 8 on the p-type InGaAs contact layer 6 on the AlGaAs LD epitaxial wafer obtained by the above epitaxial growth is performed. Carried out. Gold (Au) / gold-germanium (AuGe) / gold (Au) is sequentially deposited on the n-type GaAs substrate 1 as the n-electrode 7, and titanium (Ti) as the p-electrode 8 is deposited on the p-type InGaAs contact layer 6. ) / Platinum (Pt) / gold (Au) were sequentially deposited.

After this electrode formation process, the contact resistance between the p-electrode 8 made of Ti / Pt / Au and the p-type InGaAs contact layer 6 was evaluated by a TLM (Transmission Length Model) method. As a result, the contact resistance value in this example is 5 × 10 ⁻⁷ (Ωcm ² ), and the contact resistance value (1 × 10 ⁻⁵ (Ωcm ² )) when a p-type GaAs contact layer having a conventional structure is used. Compared with the above), it was found to be significantly smaller.

  Further, as a result of measuring the LD characteristics, a more stable current-voltage characteristic was obtained than before. Furthermore, as a result of conducting a life test of the LD, the deterioration of the LD characteristics due to continuing energization, which has been a problem in the past, was not observed in the LD of this example. In the conventional LD, impurities in the p-type cladding layer diffuse into the active layer due to the electrode activation heat treatment, and thus an abnormality is observed in the current-voltage characteristics, or crystal defects are generated and the LD characteristics are deteriorated. However, in this example, the activation heat treatment became unnecessary after the formation of the p-electrode, and it was possible to prevent them.

2 and 3 show data obtained by actually measuring the contact resistance between the p-type contact layer and the p-electrode.
FIG. 2 is a graph showing how the contact resistance changes when the In composition x of the p-type InGaAs contact layer 6 made of In _x Ga _1-x As is changed from 0 (conventional) to 0.7. It is. From this graph, the In composition x of In _x Ga _1-x As is in the range of 0.1 ≦ x ≦ 0.6, the value of the contact resistance is 1 × 10 ⁻⁵ (Ωcm ² ) or less, and x = 0. At the time of 5, the minimum value was 5 × 10 ⁻⁷ (Ωcm ² ).

FIG. 3 shows the value of the contact resistance when the carrier concentration in the p-type InGaAs contact layer 6 having an In composition of 0.5 is changed from 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ²⁰ cm ^−3. It is a graph which shows whether it becomes. As can be seen from this graph, regarding the Zn doping concentration, the carrier concentration is in the range of 5 × 10 ¹⁸ cm ^{−3 to} 5 × 10 ¹⁹ cm ⁻³ , and the contact resistance value is 1 × 10 ⁻⁶ (Ωcm ² ) or less. became.

It is sectional drawing which shows the structure where the epitaxial wafer for laser diodes and the electrode were formed in this in the embodiment and Example of this invention. It is a graph which shows the relationship between In composition of an InGaAs contact layer and contact resistance in the Example of this invention. It is a graph which shows the relationship between the carrier concentration of an InGaAs contact layer and contact resistance in the Example of this invention. It is sectional drawing which shows the structure of the conventional laser diode.

Explanation of symbols

1 n-type GaAs substrate 2 n-type GaAs buffer layer 3 n-type AlGaAs cladding layer 4 active layer 5 p-type AlGaAs cladding layer 6 p-type InGaAs contact layer 7 n-electrode 8 p-electrode

Claims (4)

On the n-type GaAs substrate, there is a light emitting portion composed of an n-type AlGaAs cladding layer, an active layer, and a p-type AlGaAs cladding layer,
An epitaxial wafer for light-emitting elements, wherein a p-type InGaAs contact layer is formed as an electrode forming layer on the p-type AlGaAs clad layer.   2. The epitaxial wafer for a light-emitting element according to claim 1, wherein the p-type InGaAs contact layer has a thickness of 10 nm to 0.2 μm.   The epitaxial wafer for light-emitting elements according to claim 1, wherein the p-type dopant of the p-type InGaAs contact layer is Zn or Mg.   A light emitting device epitaxial wafer according to claim 1, wherein an n electrode is formed on the n type GaAs substrate side, and a non-alloy type p electrode is formed on the p type InGaAs contact layer side. A light emitting element characterized by comprising:

Images