JP2008118038A - Epitaxial wafer for light emitting element, its manufacturing method, and light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epitaxial wafer for a light emitting element capable of obtaining many light emitting element chips which keep Iop at a constant value for extended hours, in other words, provide high reliability. <P>SOLUTION: An epitaxial layer 3 containing an n-type clad layer 6, active layer 8, p-type first clad layer 10, and p-type second clad layer 12 is grown on a substrate 2 using group III and group V material gas, in an epitaxial wafer 1 for a light emitting element. Here, the average value of hydrogen concentration of the epitaxial layer 3 is 9.2×10<SP>16</SP>atoms/cm<SP>3</SP>or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention mainly relates to an epitaxial wafer (hereinafter referred to as an epi-wafer) for a light-emitting element such as an LD (Laser Diode: semiconductor laser) and an LED (Light Emitted Diode), a method for manufacturing the same, and a light-emitting element.

  LDs using AlGaInP-based compound semiconductor crystals are widely used as reading light sources and writing light sources in optical disc systems such as digital versatile discs (DVD) and compact discs (CD).

  One method for growing a compound semiconductor crystal is a 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 of high-purity hydrogen carrier gas, and the source material is pyrolyzed in the vicinity of the substrate heated in the growth reactor. In this way, the compound semiconductor crystal is epitaxially grown on the substrate. An epitaxial wafer is obtained by epitaxially growing a semiconductor crystal on a substrate.

  The prior art document information related to the invention of this application includes the following.

JP-A-10-270797

  In recent years, there has been a demand for higher output of LD by increasing the writing speed of DVD and increasing the speed to double-layer writing.

  One of the characteristics of the LD, the operating current (Iop), is a forward current (for example, a bias current or a threshold current) for obtaining a prescribed optical output of the laser. It goes without saying that Iop must be kept constant even if it is operated for a long period of time, but if it is operated for several hundred hours or more, it may gradually increase. With this, LD is not useful as a product.

  In particular, if the LD has a high output, the Iop in the normal state is high, and the operation is performed in a severely thermal environment. Therefore, a severer characteristic is required for the high output LD.

  As one of the reasons why Iop becomes unstable, it is known that when the hydrogen concentration in the epitaxial layer of the epi-wafer is high, the added dopant is inactivated, so that Iop becomes unstable.

  Accordingly, an object of the present invention is to provide a light-emitting element epi-wafer that can maintain Iop at a constant value for a long time, that is, can take many light-emitting element chips with high reliability, a method for manufacturing the same, and a light-emitting element.

The present invention has been devised to achieve the above object, and the invention of claim 1 provides an n-type cladding layer, an active layer, and a p-type cladding layer on a substrate using a group III and group V source gas. An epitaxial wafer for light-emitting elements, in which an epitaxial layer containing light is grown, wherein an average value of hydrogen concentration of the epitaxial layers is 9.2 × 10 ¹⁶ atoms / cm ³ or less.

The invention according to claim 2 is the epitaxial wafer for light emitting device according to claim 1, wherein the hydrogen concentrations of the n-type cladding layer, the active layer, and the p-type cladding layer are all 9.2 × 10 ¹⁶ atoms / cm ³ or less. is there.

  The invention according to claim 3 is the epitaxial wafer for light emitting device according to claim 1 or 2, wherein the n-type cladding layer, the active layer, and the p-type cladding layer are made of AlGaInP.

  A fourth aspect of the present invention is the light-emitting element epitaxial wafer according to the first or second aspect, wherein the n-type cladding layer, the active layer, and the p-type cladding layer are made of AlGaAs.

  The invention according to claim 5 is an epitaxial layer including a group III and group V source gas, a doping source and a carrier gas supplied onto a heated substrate, and an n-type cladding layer, an active layer, and a p-type cladding layer on the substrate. In the method for manufacturing an epitaxial wafer for a light-emitting element, the supply of the group III source material is temporarily stopped, and only the group V source gas is supplied onto the substrate to reduce the average value of the hydrogen concentration of the epitaxial layer. It is a manufacturing method of the epitaxial wafer for light emitting elements.

  The invention of claim 6 is a light emitting device manufactured using the epitaxial wafer for light emitting device according to any one of claims 1 to 4.

  According to the present invention, it is possible to stabilize Iop, which is one of the characteristics of the light emitting element, and to improve reliability.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

  FIG. 1 is a structural diagram of an epitaxial wafer for light emitting devices showing a preferred embodiment of the present invention.

  As shown in FIG. 1, an epitaxial wafer 1 for a light emitting device according to this embodiment is an LD epiwafer, and a group III-V compound semiconductor crystal is grown on a substrate 2 using a group III and group V source gas. An epitaxial layer 3 is formed.

  The epitaxial layer 3 includes a buffer layer 4, a second buffer layer 5, an n-type cladding layer 6, a guide layer 7, an active layer 8, a second guide layer 9, a p-type first cladding layer 10, an etching stop layer 11, and a p-type. The second cladding layer 12, the intermediate layer 13, and the contact layer 14 are sequentially stacked.

  The buffer layer 4 and the second buffer layer 5 are formed in order to alleviate the lattice mismatch between the substrate 2 and the n-type cladding layer 6. The n-type cladding layer 6, the p-type first cladding layer 10, and the p-type second cladding layer 12 are semiconductor layers having a low refractive index and a high band gap energy formed adjacent to or close to the active layer 8. The guide layer 7 serves as a buffer layer when the active layer 8 is grown, and the second guide layer 9 serves as a buffer layer when the p-type first cladding layer 10 is grown. The intermediate layer 13 is formed in order to mitigate lattice irregularities between the p-type second cladding layer 12 and the contact layer 14. The contact layer 14 has a high carrier density and is formed to obtain ohmic contact with the electrode.

Now, in the epitaxial wafer 1 according to this embodiment, the average value of the hydrogen concentration in the epitaxial layer 3 is 9.2 × 10 ¹⁶ atoms / cm ³ or less. Since the contact layer 14 does not significantly affect the characteristics of the LD, the hydrogen concentration may exceed 9.2 × 10 ¹⁶ atoms / cm ³ .

In particular, in the case of an LD epi-wafer, the characteristics of the LD obtained from this are almost determined by the hydrogen concentration of the n-type cladding layer 6, the active layer 8, the p-type first cladding layer 10, and the p-type second cladding layer 12. The hydrogen concentration in 8, 10, and 12 is preferably 9.2 × 10 ¹⁶ atoms / cm ³ or less.

The hydrogen concentration was reduced to 9.2 × 10 ¹⁶ atoms / cm ³ or less because when the hydrogen concentration exceeded 9.2 × 10 ¹⁶ atoms / cm ³ , the added dopant was inactivated, so This is because it becomes stable.

  The n-type cladding layer 6, the active layer 8, the p-type first cladding layer 10, and the p-type second cladding layer 12 are made of AlGaInP or AlGaAs.

  When this epi-wafer 1 is made into a chip and an electrode is formed on the contact layer 14, an LD as a light emitting element is obtained.

  Next, a method for manufacturing the epi wafer 1 will be described.

  First, the substrate 2 is set in a furnace (reaction furnace) of a conventional semiconductor manufacturing apparatus such as a MOVPE apparatus. The semiconductor manufacturing apparatus is connected with gas supply means for supplying a group III and group V source gas, a doping source and a carrier gas into the furnace.

  In this state, the substrate 2 is heated, and a group III and group V source gas, a doping source and a carrier gas are supplied from the gas supply means on the heated substrate 2, and the above-described layers 4 to 14 are sequentially grown and stacked. The epitaxial layer 3 is formed by a crystal growth method such as the MOVPE method.

The temperature in the furnace during the growth of the epitaxial layer 3 or immediately after the growth (at least during the growth of the n-type cladding layer 6, the active layer 8, the p-type first cladding layer 10 and the p-type second cladding layer 12). Is maintained at a temperature equal to or higher than the temperature at the time of crystal growth, and the supply of the group III source material into the furnace is temporarily stopped, and only the group V source gas is supplied onto the substrate 2 to increase the hydrogen concentration in the epitaxial layer 3. The average value is lowered to 9.2 × 10 ¹⁶ atoms / cm ³ or less.

However, the group V gas contained in the epitaxial layer 3 grown immediately before is included in the group V gas supplied at this time. For example, if an AlGaInP layer is grown immediately before, PH ₃ containing P element or the like is flowed, and AsH ₃ is flowed in the case of an AlGaAs layer. At this time, a carrier gas (an inert gas such as Ar, N ₂ , and He other than H ₂ ) may be supplied together with the group V gas.

  In the present embodiment, when the heat treatment condition is an AlGaInP layer, the heater set temperature in the semiconductor manufacturing apparatus is 680 to 720 ° C. for 0.5 to 10 minutes, and in the case of the AlGaAs layer, the heater set temperature is 750. It was made into 0.5 to 10 minutes at -800 degreeC.

Here, the hydrogen concentration in the epitaxial layer 3 is measured by SIMS analysis. SIMS is Secondary Ion Mass Spectrometry = secondary ion mass spectrometry. In SIMS analysis, materials such as O ²⁺ and Cs ⁺ are irradiated on the surface of the material, and secondary ions ionized in the sputtered atoms are subjected to mass analysis, thereby analyzing the components and impurities of the substance. Is the method. Since the material surface is sputtered by the ions, an element distribution in the depth direction from the surface of the sample can also be obtained.

  The operation of this embodiment will be described.

In the epitaxial wafer 1, the average value of the hydrogen concentration of the epitaxial layer 3 is 9.2 × 10 ¹⁶ atoms / cm ³ or less.

  The inventor has found that the hydrogen concentration in the epitaxial layer 3 is changed by maintaining a high-temperature atmosphere in which crystal growth is not performed during or immediately after crystal growth as in the manufacturing method described above. In other words, during the crystal growth or immediately after the growth, the supply of the group III raw material into the furnace is stopped, and only the group V raw material is supplied into the furnace and kept for several minutes. The temperature in the furnace is kept above the temperature at the time of growth. The hydrogen concentration in the epitaxial layer 3 varies depending on the timing and time of holding the temperature of the group V source atmosphere (hereinafter referred to as heat treatment).

This is because heat treatment causes the group V atom in the group V raw material to become a trivalent anion, and the anion adsorbs radical H ⁺ , so that hydrogen inevitably mixed in the epitaxial layer 3 is expelled, This is because the hydrogen concentration in the epitaxial layer 3 is lowered.

  As a result, the epiwafer 1 has a low hydrogen concentration that causes the Iop to become unstable, so that the added dopant is prevented from being deactivated, and Iop, which is one of the LD characteristics, is kept at a constant value for a long time. It is possible to stabilize the Iop and improve the reliability of the epi-wafer. Therefore, the epitaxial wafer 1 can take many LD chips with high reliability.

In particular, if the hydrogen concentration of the n-type cladding layer 6, the active layer 8, the p-type first cladding layer 10, and the p-type second cladding layer 12 are all 9.2 × 10 ¹⁶ atoms / cm ³ or less, Iop is reduced. It is possible to further stabilize and improve the reliability of the epi-wafer 1.

  In the above-described embodiment, an example of an LD epi-wafer has been described as the epi-wafer 1. However, the epi-wafer 1 and its manufacturing method according to this embodiment can also be used for an LED epitaxial wafer manufactured by the MOVPE growth method.

  The epiwafer 1 and the manufacturing method thereof according to the present embodiment can be applied not only to AlGaInP and AlGaAs, but also to GaN epiwafers used for blue-violet LDs, blue LEDs, and the like.

(Example)
By introducing a group III organometallic source gas and a group V source gas into the reaction furnace as a mixed gas of high-purity hydrogen carrier gas, the source is thermally decomposed near the substrate 2 heated in the reaction furnace, The epitaxial layer 3 was epitaxially grown on the substrate 2 by the MOVPE method to produce an epitaxial wafer having the structure shown in FIG. Here, n-type and p-type are denoted by n- and p-, respectively. Those not added with impurities are called undoped and indicated by un-.

TMG (trimethylaluminum) as the Al source, TMI (trimethylindium) as the In source, AsH ₃ (arsine) as the As source, PH ₃ (phosphine) as the P source, Si ₂ as the Si source DMZ (dimethylzinc) was used as a Zn source which is H ₆ (disilane) and p-type impurities.

More specifically, on the n-type conductive GaAs substrate, n-type GaAs (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) having a thickness of 200 nm as a buffer layer, and n-type Ga _{0.51 having a} thickness of 200 nm as a second buffer layer. In _0.49 P (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) was grown. On top of that, n-type (Al _0.68 Ga _0.32 ) _0.51 In _0.49 P (carrier concentration 7.5 × 10 ¹⁷ cm ⁻³ ) having a thickness of 2500 nm as an n-type cladding layer and no impurity having a thickness of 35 nm as an undoped guide layer are added. (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P was grown. The active layer has a multi-quantum well (MQW: quantum well) structure with Ga _0.51 In _0.49 P as a well and (Al _0.5 Ga _0.5 ) _0.51 In _0.49 P as a barrier, and no impurity is added. A crystal similar to the undoped guide layer was grown as a second undoped guide layer on the active layer with a thickness of 70 nm. Then, (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P (carrier concentration 9.1 × 10 ¹⁷ cm ⁻³ ) having a thickness of 300 nm is used as the p-type first cladding layer, and Ga _0.55 In _0.45 P to which no impurity is added is used as the etching stop layer. A thickness of 10 nm was grown. On the etching stop layer, the same crystal as the p-type first cladding layer was grown as a p-type second cladding layer having a thickness of 1500 nm. Further, a p-type Ga _{0.5In 0.49} P (carrier concentration of 1.5 × 10 ¹⁸ cm ⁻³ ) is grown to a thickness of 30 nm as an intermediate layer for relaxing the lattice mismatch between the p-type second cladding layer and the contact layer. It was. A p-type high concentration GaAs (carrier concentration 5.0 × 10 ¹⁸ cm ⁻³ ) having a thickness of 300 nm was grown as a contact layer on the uppermost layer.

Thereafter, heat treatment was performed to produce an LD epiwafer. The heat treatment was set to the same temperature as the temperature at which the p-type first cladding layer was grown, and the supply of the group III material into the furnace was stopped and only the group V material was supplied. The group V raw material was PH ₃ and the heat treatment time was 5 minutes.

(Comparative example)
An LD epiwafer was produced in the same manner as in the example without performing any heat treatment.

When the hydrogen concentration of the epi layer was compared, the example was 7.2 × 10 ¹⁶ atoms / cm ³ , and the comparative example was 6.4 × 10 ¹⁷ atoms / cm ³ . The hydrogen concentration was measured in all epi layers except the contact layer, and the average value of all measured values was taken.

  In order to eliminate the influence of variation in one-time growth, each of the examples and comparative examples was alternately performed three times.

  The same number of LD chips were produced from three epi wafers for each of the example and comparative example, and the characteristics of the LD were evaluated.

  As a result, in the high temperature Iop reliability test at 70 ° C. for 1000 hours, the reliability survival rate of the comparative example was 59%, while the example was improved to 90%.

  In addition, an epi-wafer having a changed hydrogen concentration was produced by changing the heat treatment conditions. The result of comparing the LD characteristics obtained from each epi-wafer is shown in FIG. 3 together with the results of Examples and Comparative Examples.

  In FIG. 3, the epi-wafer according to the present embodiment is indicated by ●, and other comparative examples and conventional examples are indicated by ■. (I) to (v) in FIG. 3 show heat treatment conditions ((heater set temperature) × (heat treatment time)), (i) is 610 ° C. × 30 seconds, (ii) is 650 ° C. × 30 seconds, ( iii) is 690 ° C. × 30 seconds, (iv) is 690 ° C. × 10 minutes, and (v) is 730 ° C. × 5 minutes.

As shown in FIG. 3, it was found from this result that the LD characteristics were improved, that is, the reliability test result of Iop was improved when the hydrogen concentration in the epiwafer was 9.2 × 10 ¹⁶ atoms / cm ³ or less. .

1 is a structural diagram of an epitaxial wafer for light-emitting elements showing a preferred embodiment of the present invention. It is a structural diagram of the epitaxial wafer for light emitting elements used in the examples. It is a figure which shows the result of having put together the reliability test survival rate of Iop when changing the hydrogen concentration in an epilayer for optimal condition confirmation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Epitaxial wafer 2 for light emitting elements Substrate 3 Epitaxial layer 4 Buffer layer 5 Second buffer layer 6 N-type cladding layer 7 Guide layer 8 Active layer 9 Second undoped guide layer 10 P-type first cladding layer 11 Etching stop layer 12 P-type Second cladding layer 13 Intermediate layer 14 Contact layer

Claims (6)

In an epitaxial wafer for a light emitting device in which an epitaxial layer including an n-type cladding layer, an active layer, and a p-type cladding layer is grown on a substrate using a group III and group V source gas, an average value of hydrogen concentration of the epitaxial layer An epitaxial wafer for a light-emitting element, characterized in that is 9.2 × 10 ¹⁶ atoms / cm ³ or less. The epitaxial wafer for a light-emitting element according to claim 1, wherein the hydrogen concentration of each of the n-type cladding layer, the active layer, and the p-type cladding layer is 9.2 × 10 ¹⁶ atoms / cm ³ or less.   The epitaxial wafer for light-emitting elements according to claim 1, wherein the n-type cladding layer, the active layer, and the p-type cladding layer are made of AlGaInP.   The epitaxial wafer for light-emitting elements according to claim 1 or 2, wherein the n-type cladding layer, the active layer, and the p-type cladding layer are made of AlGaAs.   A group III and group V source gas, a doping source and a carrier gas are supplied onto a heated substrate, and an epitaxial layer including an n-type cladding layer, an active layer, and a p-type cladding layer is grown on the substrate. In the wafer manufacturing method, the supply of the group III source material is temporarily stopped, and only the group V source gas is supplied onto the substrate to reduce the average value of the hydrogen concentration of the epitaxial layer. Epitaxial wafer manufacturing method.   A light emitting device manufactured using the epitaxial wafer for light emitting device according to claim 1.

Images