DE10306309A1 - Simple and cost effective process for preparation of a radiation emitting semiconductor chip based on AlGaInP useful in production of light emitting diodes (LED) - Google Patents

Abstract

Preparation of a radiation emitting semiconductor chip based on AlGaInP by the steps: preparation of substrate (12), application of a semiconductor on the substrate, which contains a photon emitting active layer (22), and application of a transparent decoupling layer (16) which includes compounds of given formula containing Ga, In, Al, and P, where substrate (12) is formed from germanium and layer (16) is applied at a maximum temperature of 800 [deg] C. An independent claim is included for the above radiation emitting semiconductor as described.

Description

The invention relates to a method for producing an electromagnetic radiation-emitting semiconductor chip based on AlGaInP, comprising the steps of: providing a substrate; Applying a semiconductor layer sequence to the substrate which contains a photon emitting active layer; and applying a transparent coupling-out layer comprising Ga _X (In _y Al _1-y ) _1-x P with 0 <x ≤ 0.2 and 0 ≤ y 1 1. The invention also relates to an AlGaInP-based semiconductor radiation-emitting semiconductor chip with a substrate, a semiconductor layer sequence applied to the substrate with a photon-emitting active layer and a transparent coupling-out layer arranged on the active layer and comprising GaP.

In the present case, the materials based on InGaAlP include all mixed crystals with a composition that falls under the formula In _X Ga _Y Al _1-xy P with 0 ≤ x ≤ 1.0 ≤ y ≤ 1 and x + y ≤ 1. The AlGaInP-based semiconductor chips emitting electromagnetic radiation include all semiconductor chips in which the semiconductor layer sequence in which an electromagnetic radiation-generating layer is located has at least a substantial proportion of material based on InGaAlP and the properties of the radiation emitted by the semiconductor chip from the latter material based on InGaAlP are at least essentially determined.

The AlGaInP material system is for the application very interesting in light emitting diodes, because its band gap due to the variation of the Al share over one wide range from 1.9 eV to 2.2 eV is adjustable. That means, that light emitting diodes made from this material in the color range from red to green can.

• – Es muß eine Gitterkonstante besitzen, die es ermöglicht, die Materialsysteme AlGaInP und AlGaAs einkristallin abzuscheiden,
• – es muß bei den verwendeten Prozeßtemperaturen noch ausreichend fest sein, und
• – es muß in ausreichend guter Qualität kommerziell erhältlich sein.

In order to produce such light-emitting diodes by means of epitaxy, a substrate is required on which the various semiconductor layers of the semiconductor layer sequence can be deposited as single-crystal as possible. A substrate for the epitaxy of AlGaInP-based LEDs should meet the following conditions:

• - It must have a lattice constant that enables the AlGaInP and AlGaAs material systems to be deposited in single crystals,
• - It must still be sufficiently firm at the process temperatures used, and
• - It must be commercially available in sufficiently good quality.

All the conditions mentioned will of GaAs substrates. Therefore, GaAs is used worldwide as a substrate for AlGaInP light emitting diodes. Under the point of view of economical manufacture of the light-emitting diodes However, GaAs substrates have the disadvantage that they are very expensive. Other Substrate materials either have a large lattice mismatch or are for the common process steps not suitable.

The invention is therefore the object to provide a method of the type mentioned at the outset, which is a technically simple and inexpensive manufacture of a radiation-emitting AlGaInP-based semiconductor chips allowed.

This task is accomplished through a process solved with the features of claim 1. Further advantageous Ausgestaltun conditions and further developments of the invention result from subclaims 2 to 7 and 9.

An electromagnetic radiation emitting semiconductor chip according to the inventive method is producible, is the subject of claim 8. Advantageous embodiments and developments of the semiconductor chip according to the invention are the subject of subclaim 9.

According to the invention in a manufacturing process of the type mentioned in the introduction that the substrate essentially Germanium exhibits and that the transparent coupling-out layer applied at low temperature becomes. Germanium has one with the material systems AlGaInP and AlGaAs well tolerated Lattice constant and is commercially available in high quality. About that addition is the price for a germanium substrate only about half the price of a GaAs substrate, so that at Manufacturing process great Saving potential arises.

The lower thermal stability of germanium compared to GaAs, this takes account of the fact that the critical step of growing the gallium phosphide comprehensive transparent coupling-out layer is carried out at a low temperature, where the germanium substrate is still of sufficient strength having.

In a preferred embodiment of the method according to the invention it is provided that the transparent coupling-out layer is applied using tertiary butylphosphine (TBP, (C ₄ H ₉ ) PH ₂ ) as the phosphorus source. Conventional AlGaInP-based light-emitting diodes typically use a light coupling-out layer made of GaP, which is deposited epitaxially using phosphine (PH ₃ ) at a temperature above 800 ° C. Such temperatures in the reactor are too high for germanium substrates. In contrast, the use of tertiary butylphosphine as a phosphorus source enables a high quality light decoupling layer to be deposited at significantly lower process temperatures.

In particular, it is particularly expedient to use the transparent coupling-out layer at a temperature temperature below 780 ° C, preferably below 750 ° C.

It is particularly preferred if the transparent coupling-out layer at a temperature of about 700 ° C applied becomes.

Likewise, it is often convenient to transparent coupling-out layer using trimethyl gallium as a source of gallium.

With a typical lateral dimension the active layer of A = 250 μm the thickness of the coupling-out layer between about 1 μm and about 10 μm is then preferred between about 2 μm and about 10 μm selected.

In an expedient embodiment of the method according to the invention becomes the transparent coupling-out layer by means of organometallic vapor phase epitaxy (OMVPE) grew up.

The V / III ratio is growing up the transparent coupling-out layer advantageously to a value of 5 to 20, preferably set from about 10.

Further advantageous configurations, Features and details of the invention emerge from the dependent claims Description of the embodiment and the drawing.

Further advantages, preferred embodiments and further developments of the invention result from the following explanation of an embodiment in connection with the drawing. It is only for understanding the invention essential elements shown.

The only figure shows a schematic representation a sectional view of a radiation-emitting semiconductor chip according to an embodiment the invention.

1 shows a sectional view with a general 10 designated LED chip based on AlGaInP 10 in a schematic representation.

The LED chip 10 comprises a germanium substrate 12 on which a semiconductor layer sequence 14 is trained. The semiconductor layer sequence 14 is a double heterostructure in the exemplary embodiment, which is an active, photon-emitting AlGaInN-based n-type layer 22 which is enclosed by an AlGaInN-based n-type cladding layer below the active layer and an AlGaInN-based p-type cladding layer above the active layer. Such structures and layer sequences are known to the person skilled in the art and are therefore not explained in more detail here. As is known in the prior art, the layers mentioned are doped to the desired impurity content with suitable p-dopants such as Zn, C or Mg or with suitable n-dopants such as Te, Se, S and Si.

The active semiconductor layer sequence 14 can alternatively have a multi-quantum well structure, as are also known, for example, from the prior art.

On top of the p-type AlGaInP cladding layer is a thick light decoupling layer 16 from Ga _X In _y Al _1-y ) _1-x P with 0 <x ≤ 0.2 and 0 ≤ y ≤ 1. Since the band gap of the coupling-out layer is larger than that of the active layer, the light coupling-out layer is 16 for one in the active layer sequence 14 generated electromagnetic radiation permeable.

The current required for the operation of the LED chip is the active layer of the LED chip 10 in the present case via a front contact 18 and a back contact 20 fed. Alternatively, the contacts can also be arranged differently than shown in the exemplary embodiment.

The light decoupling layer 16 is applied by means of organometallic vapor phase epitaxy (OMVPE). Tertiary butylphosphine (TBP, (C ₄ H ₉ ) PH ₂ ) is used as the phosphorus source and trimethylgallium is used as the gallium source, and a V / III flow ratio of about 10 is selected. In the exemplary embodiment, the growth temperature is 720 ° C., a temperature at which the germanium substrate in the reactor is still sufficiently solid.

In the exemplary embodiment, the layer sequence has 14 a cross section of 250 μm × 250 μm and a layer thickness between 2 and 10 μm.

The in the description above, in the drawing and in the claims disclosed features of Invention can both individually and in any combination for the realization of the Invention to be essential.

Claims (9)

Method for producing a radiation-emitting semiconductor chip based on AlGaInP with the method steps: - provision of a substrate ( 12 ); - Applying a semiconductor layer sequence to the substrate, which has a photon emitting active layer ( 22 ) contains; and - applying a transparent coupling-out layer ( 16 ), which comprises Ga _X (In _y Al _1-y ) _1-x P with 0 <x ≤ 0, 2 and 0 ≤ y ≤ 1, characterized in that - the substrate ( 12 ) is essentially made of germanium and - the transparent coupling-out layer ( 16 ) is applied in a temperature range up to a maximum of 800 ° C. Method according to claim 1, characterized in that the transparent coupling-out layer ( 16 ) is applied using tertiary butylphosphine as a source of phosphorus. Method according to claim 1 or 2, characterized in that the transparent coupling-out layer ( 16 ) is applied at a temperature below 780 ° C, preferably below 750 ° C. Method according to one of the preceding claims, characterized in that the transparent coupling-out layer ( 16 ) is applied at a temperature of about 700 ° C. Method according to one of the preceding claims, characterized in that the transparent coupling-out layer ( 16 ) is applied using trimethyl gallium as the gallium source. Method according to one of the preceding claims, characterized in that the transparent coupling-out layer ( 16 ) is grown using organometallic vapor phase epitaxy (OMVPE). A method according to claim 6, characterized in that the transparent coupling-out layer ( 16 ) is grown at a V / III ratio of 5 to 20, preferably about 10. Radiation-emitting semiconductor chip based on AlGaInP with - a substrate ( 12 ); A semiconductor layer sequence applied to the substrate ( 14 ) with a photon emitting active layer ( 22 ); and - one on the semiconductor layer sequence ( 14 ) arranged transparent coupling-out layer ( 16 ), which comprises Ga _x (In _y Al _1-y ) _1-x P with 0 <x ≤ 0.2 and 0 ≤ y ≤ 1, characterized in that - the substrate ( 12 ) is formed from germanium. Radiation-emitting semiconductor chip according to one of the preceding claims, characterized in that the transparent coupling-out layer ( 16 ) has a thickness between 1 μm and 10 μm, in particular between 2 μm and 10 μm.