WO2002065555A1

WO2002065555A1 - Radiation emitting semiconductor bodies and method for the production thereof

Info

Publication number: WO2002065555A1
Application number: PCT/DE2001/004293
Authority: WO
Inventors: Stephan Lutgen
Original assignee: Osram Opto Semiconductors Gmbh
Priority date: 2000-11-15
Filing date: 2001-11-15
Publication date: 2002-08-22
Also published as: DE10056476B4; TW540164B; DE10056476A1

Abstract

The invention relates to a radiation producing layer sequence (2) grown directly on a window layer (3), which has one or a plurality of successive AlgaAs layers (4, 5, 6). The AlGaAs layers are produced by liquid phase epitaxy or a similar method and have an AI content remotely from the layer sequence (2), wherein the AlGaAs is permeable to the radiation produced. The Al content diminishes in each of the AlGaAs layers (4, 5, 6) in the direction of the active layer sequence (2). The window layer (3) alternatively consists of a self-supporting AlGaAs expitaxial substrate (7) having an Al content in which AgGaAs is permeable to the radiation produced.

Description

description

Radiation-emitting semiconductor body and method for its production

The invention relates to a radiation-emitting semiconductor body according to the preamble of claim 1. It also relates to a method for producing such a semiconductor body.

A light-emitting diode with a radiation-transmissive window is known for example from US 5,869,849. This describes a semiconductor chip with an active layer sequence on the basis of AlGalnP, which has a window made of GaP, which is applied by means of wafer bonding technology.

US Pat. No. 5,661,742 describes a light-emitting diode structure which has an epitaxially applied InGaP window layer.

Wafer-bonded window layers cause a considerable additional technical outlay and epitaxially applied GaP-based ones due to the wafer-bonding process steps required in addition to the epitaxy processes

Window layers can only be applied to GaP-based or similar active layer sequences.

In the present context, GaP-based layers are to be understood to mean all Am-Bv semiconductor compositions which have Ga at the A place and P at the B place. This includes in particular corresponding ternary and. Quaternary compounds, such as InGaAlP, InGaP and GaAlP, as well as GaP itself.

For a series of active or passive optoelectronic layer sequences, which are particularly deposited on GaAs substrates. no satisfactory window layers are known so far, such as IR emitting or - detecting layer sequences based on GaAs.

The object of the present invention is to provide a radiation-emitting semiconductor body of the type mentioned at the outset, in particular an infrared-emitting semiconductor body, which has a window layer which can be produced inexpensively.

Furthermore, a method for producing such a component and a substrate is to be specified.

The first-mentioned object is achieved by a semiconductor body with the features of claim 1 or claim 11. Advantageous refinements and developments are the subject of dependent claims 2 to 10 and 12 to 16.

A method for producing a semiconductor body according to patent claim 1 and the subclaims which refer back to it is the subject of patent claim 17. Preferred developments of this method are specified in subclaims 18 and 19. A method for producing a substrate according to the invention is the subject of patent claim 22.

A method for producing a semiconductor body according to claim 11 and the subclaims which refer back to it is the subject of claim 20. A preferred embodiment of this method is the subject of

Subclaim 21. A method for producing a substrate is the subject of claim 22. A substrate produced according to the invention is the subject of claim 23.

According to the invention, in the case of a radiation-emitting semiconductor body of the type mentioned at the beginning, the window layer one or a plurality of successive AlGaAs layers which are produced by means of liquid phase epitaxy or a similar method and which each have an Al content at a distance from the layer sequence, at which AlGaAs is transparent to the radiation generated, and the Al Content in each of the AlGaAs layers decreases in the direction of the radiation-generating layer sequence.

In the window layer, the AlGaAs layer arranged adjacent to the layer sequence preferably has an Al content in the transition region to the layer sequence, at which AlGaAs is essentially impermeable to the radiation generated. This transition region is preferably between about 10 nm to 30 nm thick.

The window layer is further preferably particularly epitaxially grown by means of liquid phase epitaxy or a similar method and the layer sequence is epitaxially grown by means of gas phase epitaxy, in particular by means of metal organ-safe gas phase epitaxy or molecular beam epitaxy or the like.

Further advantageous developments of this arrangement are the subject of dependent claims 2 to 9.

According to the second embodiment of the invention, the window layer is formed by a self-supporting growth epitaxial substrate which essentially consists of AlGaAs and has an Al content in which AlGaAs is transparent to the radiation generated.

Particularly advantageous developments of this arrangement are the subject of dependent claims 12 to 16.

The invention can also be used advantageously for the production of radiation-detecting components. The invention and its advantages are explained below using several exemplary embodiments in conjunction with FIGS. 1 a to 3 b. Show it:

Figure la shows a basic representation of the layer sequence of a semiconductor body according to the invention;

Figure lb is a schematic representation of a diagram in which the Al content in the semiconductor body according to Figure la is plotted against the layer thickness;

FIGS. 2a to 2a show a schematic representation of a process sequence for producing a semiconductor body according to FIG. 1a;

FIG. 3a shows a basic representation of the layer sequence of a further semiconductor body according to the invention; and

FIG. 3b shows a schematic representation of a diagram in which the Al content in the semiconductor body according to FIG. 3a is plotted over the layer thickness.

In the case of a semiconductor body according to FIG. 1 a, a radiation-generating layer sequence 2 (hereinafter referred to only briefly as “active layer sequence”) has grown epitaxially on a window layer 3, which consists of three successive AlGaAs layers 4, 5, 6. The active layer sequence 2 has, for example, a luminescence diode structure or a vertically surface-emitting laser diode structure (for example a so-called VCSEL (Vertical Cavity Surface Emitting Laser) - or VECSEL (Vertical External Cavity Surface Emitting Laser) structure). It is particularly preferably one based on GaAs manufactured infrared emitting semiconductor structure.

The active layer sequence 2 is preferably produced by means of organometallic vapor phase epitaxy. The structures mentioned above for the active layer sequence 2 are well known and therefore do not require any detailed explanation at this point.

The three successive AlGaAs layers 4, 5, 6 are produced by means of liquid phase epitaxy and each have an Al content that changes over the layer thickness. Each of the AlGaAs layers 4, 5, 6 has an Al content on the side remote from the active layer sequence 2, which is clearly above the Al content, with the AlGaAs essentially for the radiation generated in the active layer sequence 2 is impermeable. This limit of the Al content is only briefly referred to as the transmission limit in the following.

From the side lying away from the active layer sequence 2 towards the layer sequence 2, the Al content in each of the AlGaAs layers 4, 5, 6 continuously decreases. On the side facing the active layer sequence 2, the Al content, if at all, is only below the transmission limit for a layer thickness of 10 nm to 30 nm.

Consequently, the Al content, as shown schematically in the diagram in FIG. 1b, has a sawtooth-like course over the three successive AlGaAs layers 4, 5, 6. There, the direction of growth is plotted on the horizontal axis and the Al content on the vertical axis, and the transmission limit of the Al content is indicated by the dashed line labeled TG.

It preferably has adjacent to the active layer sequence

2 lying AlGaAs layer 6 in the transition area to layer sequence 2 over a layer thickness which is between 10 nm and 30 nm, an Al content which is below the transmission limit. This has the advantage that an oxidation of the Al-containing layer in air can be prevented, which, among other things, an undesired electrically insulating Barrier layer for the subsequently applied layer sequence 2 would represent.

The total layer thickness d of all AlGaAs layers 4, 5, 6 is preferably between approximately 100 μm and 200 μm. Together, they represent a mechanically stable support for the active layer sequence 2, the total thickness of which is generally in the range of only a few μm.

The AlGaAs layers 4, 5, 6 are preferably produced by means of liquid phase epitaxy (LPE) and are typically each up to 50 μm thick. Any Al depletion in the direction of growth that occurs in liquid phase epitaxy is rendered "harmless" with the aid of the AlGaAs multiple structure according to the invention. On the basis of an AlGaAs multiple structure according to the invention with two or more AlGaAs layers, multiple LPE growth or -boot process self-supporting transparent AlGaAs-LPE layers with larger layer thicknesses. Typical total layer thicknesses between 100-200μm with sufficient mechanical stability can be achieved very easily in this way. The deposition temperatures are typically 700-1000 ° C.

Overall, the Al content in the AlGaAs multiple structure 4,5,6 must not decrease over greater layer thicknesses (> 100 nm) below the transparency range for the light generated in the active, so that there is no significant (> 3%) absorption of the emitted light in the AlGaAs layers can take place. Thin layers (typically 10-30nm) with an aluminum content below the transparency range (compare, for example, the transition region 10 encircled in FIG. so that oxidation of the Al-containing layer in air can be prevented, which, among other things, prevents undesired electrically insulating barrier layer to the subsequent epitaxial layers of the active layer sequence 2 would represent.

In the method schematically illustrated in FIGS. 2a to 2e for producing a radiation-emitting semiconductor body according to FIGS. 1a and 1b, three AlGaAs layers 4 are first successively formed on an epitaxial substrate 7, which consists, for example, of GaAs or another suitable material, by means of liquid phase epitaxy. 5.6 grew up. These process steps take place at a first process temperature, which is preferably between approximately 700 ° C. and approximately 1000 ° C.

The layers of the active layer sequence 2 are subsequently applied to the AlGaAs multilayer structure 4, 5, 6 by means of organometallic gas phase epitaxy or molecular beam epitaxy at a second process temperature that is lower than the first process temperature and in the range between approximately 400 ° C. and approximately 800 ° C. lies.

Electrical contact layers 8 and 9 are subsequently produced on the mutually opposite main surfaces of the semiconductor body 1. With such an arrangement of the electrical contact layers, the AlGaAs layers 4, 5, 6 are doped in an electrically conductive manner.

Optionally, the epitaxial substrate 7 is removed beforehand in order to further reduce the radiation absorption within the substrate region of the semiconductor body, that is to say outside the active layer sequence 2.

The rear-side contact 9 is preferably designed to be reflective if a radiation coupling-in or coupling-in is provided exclusively to the front and to the side or from the front and from the side. The semiconductor layer sequence according to the invention is particularly preferably suitable for the production of semiconductor bodies in which the wavelength of the radiation to be coupled in or out via the window layer 3 is in the infrared or red spectral range and below 870 nm. The absorption edge of the window layer 3 is advantageously adjusted with the aid of the varying Al content overall to a shorter wavelength than the wavelength of the radiation to be coupled in or out.

In the semiconductor body according to FIG. 3a, a window layer 3 is formed by a self-supporting epitaxial substrate 11, which essentially consists of AlGaAs and has an Al content in which AlGaAs is transparent to the radiation generated. Compare the diagram in FIG. 3b in which the direction of growth is plotted on the horizontal axis and the Al content is plotted on the vertical axis and the transmission limit of the Al content is indicated by the dashed line with the designation TG.

Such an epitaxial substrate 11 is advantageously produced using a vertical gradient freeze (VGF) process.

In order to obtain a chip structure with opposing electrical contacts, the epitaxial substrate 11 is preferably doped in an electrically conductive manner.

This semiconductor layer sequence according to the invention, like the one described above, is particularly preferably suitable for the production of semiconductor bodies in which the wavelength of the radiation to be coupled in or out via the window layer 3 is less than 870 nm in the infrared and red spectral range. The absorption structure of the window layer 3 is set to a shorter wavelength than the wavelength of the radiation to be coupled in or out. The layer sequence according to the invention can advantageously be used both for a vertically surface-emitting semiconductor laser structure and for luminescence diode structures.

Depending on the component structures, the semiconductor layers of exemplary semiconductor bodies according to the invention consist of:

- In the case of light-emitting diodes (LEDs), typically made of electrically conductive layers with possibly additional Bragg reflection layers which are transparent to the light generated in the active layer. The active layer usually consists of one or more quantum films. A layer sequence arranged on the active layer can include consist of electrically conductive layers for an ohmic connection with an electrical metal contact.

Due to the transparency of the AlGaAs multilayer structure or the AlGaAs epitaxial substrate, part of the low-energy light from the active layer can be reflected via the back of the AlGaAs window layer or by means of a reflective back contact on the back of the AlGaAs window layer and partly to the side and / or be coupled forward. With the help of the transparent AlGaAs multilayer structure or the transparent AlGaAs epitaxial substrate, backward-emitting LED structures can consequently also be produced. The active LED structure is epitaxied directly on the window layer, that is to say on the AlGaAs multilayer structure or the AlGaAs epitaxial substrate, without having to produce a transparent, partially electrically conductive substrate carrier contact by means of subsequent technically complex wafer bonding or fusing.

- In the case of resonant light-emitting diodes (RCLEDs), typically made of electrically conductive layers with feedback Bragg reflection layers with a low number of periods (typ. 5

tion in a high quality resonator above the threshold current.

The active layer usually consists of one or more quantum films. The total layer thickness is an integral multiple of half the emission wavelength. The position of the quantum films is in the belly of the standing wave field.

The subsequent layer sequence consists of phase-matched Bragg reflection layers (typically 27 periods), which serve as high-quality reflectors (R is approx. 0.99) for the light generated in the active layer. These layers can include consist of electrically conductive layers for a later ohmic metal contact.

Due to the transparency of the AlGaAs multilayer structure or the AlGaAs epitaxial substrate, the part of the low-energy laser radiation that leaves the laser resonator due to the lower reflectivity of the feedback Bragg reflector layers is coupled out without absorption via the AlGaAs back layers. With the help of the transparent AlGaAs multilayer structure or the AlGaAs epitaxial substrate, back-emitting VCSEL structures can be produced. The active VCSEL structure is epitaxied directly on the window layer, that is to say on the AlGaAs multilayer structure or the AlGaAs epitaxial substrate, without having to produce a transparent, partially electrically conductive substrate carrier contact by means of subsequent technically complex wafer bonding or fusing.

Claims

claims

1. Radiation-emitting semiconductor body (1) with a radiation-generating layer sequence (2) and a window layer (3) that is at least partially transparent to the generated radiation, characterized in that the window layer (3) comprises a plurality of successive AlGaAs layers (4, 5.6), which are produced by means of liquid phase epitaxy or a similar method and which, apart from the layer sequence (2), each have an Al content at which AlGaAs is transparent to the radiation generated, and the Al content in each of the AlGaAs -Layers (4,5,6) decreases in the direction of the radiation-generating layer sequence (2).

2. Radiation-emitting semiconductor body (1) according to claim 1, characterized in that the AlGaAs layer (6) closest to the layer sequence (2) has a passivation layer in the transition region to the layer sequence (2).

3. Radiation-emitting semiconductor body (1) according to claim 1, characterized gekennz ei chnet that s the AlGaAs layer (6) closest to the layer sequence (2) in the transition region to the layer sequence (2) has an Al content, in which AlGaAs in an oxygen-containing atmosphere not or only slightly oxidized, so that it serves as a passivation layer.

4. Radiation-emitting semiconductor body (1) according to claim 3, characterized in that the s the layer thickness of the transition region is between approximately 10 nm to 30 nm.

5. Radiation-emitting semiconductor body (1) according to one of the preceding claims, characterized in that the wavelength of a radiation that is to be coupled in or out via the window layer (3) is less than 870 nm and that an absorption edge of the window layer (3) is of the varying Al content is at a shorter wavelength.

6. Radiation-emitting semiconductor body (1) according to one of the preceding claims, characterized in that the AlGaAs layers (4, 5, 6) are doped in an electrically conductive manner.

7. Radiation-emitting semiconductor body (1) according to one of the preceding claims, characterized in that the window layer (3) has a thickness of more than 5 μm.

8. Radiation-emitting semiconductor body (1) according to claim 7, characterized in that the window layer (3) has a self-supporting substrate with a thickness between approximately 100 μm and approximately 100 μm.

9. radiation-emitting semiconductor body (1) according to any one of the preceding claims, characterized gekennze i chnet that s the window layer (3) by means of liquid phase epitaxy or the like and the layer sequence (2) by means of gas phase epitaxy, in particular by means of metal-organ-safe gas phase epitaxy or molecular beam epitaxy, or the like who grew up epitaxially.

10. Radiation-emitting semiconductor body (1) according to one of claims 2 to 9, characterized gekennze i chnet that s instead of the plurality of successive AlGaAs layers (4,5,6) is provided a single AlGaAs layer which by means of liquid phase epitaxy or a method of the same type is produced and which, removed from the layer sequence (2), has an Al content in which AlGaAs is transparent to the radiation generated, and the Al content decreases in the direction of the radiation-generating layer sequence (2).

11. Radiation-emitting semiconductor body (1) with a radiation-generating layer sequence (2) and a window layer (3) which is at least partially permeable to the generated radiation, characterized in that the window layer (3) is formed by a self-supporting epitaxial substrate (11) , which consists essentially of AlGaAs and has an Al content at which AlGaAs is transparent to the radiation generated.

12. Radiation-emitting semiconductor body (1) according to claim 11, characterized in that the wavelength of a radiation to be coupled in or out via the window layer (3) is less than 870 nm and there is an absorption edge of the window layer (3) at one shorter wavelength.

13. Radiation-emitting semiconductor body (1) according to claim 11 or 12, characterized in that the epitaxial substrate by means of vertical grading Freece process is made.

14. Radiation-emitting semiconductor body (1) according to one of the preceding claims, characterized in that the window layer (3) is doped in an electrically conductive manner.

15. Radiation-emitting semiconductor body (1) according to one of the preceding claims, characterized in that the layer sequence (2) has a vertically surface-emitting semiconductor laser structure.

16. Radiation-emitting semiconductor body (1) according to one of the preceding claims, characterized in that the layer sequence (2) has a luminescent diode structure.

17. A method for producing a radiation-emitting semiconductor body (1) according to one of claims 1 to 10 or according to one of claims 14 to 16 with reference to one of claims 1 to 10, characterized i chne t by the steps: a) providing an epitaxial substrate ( 7), b) growing the AlGaAs layers (4,5,6) by means of liquid phase epitaxy on the epitaxial substrate (7) at a first process temperature; c) growing the layer sequence (2) on the AlGaAs layers (4,5,6) by means of organometallic gas phase epitaxy or molecular beam epitaxy at a second process temperature.

18. The method according to claim 17, characterized in that the first process temperature between 700 ° C and 1000 ° C. and the second process temperature is between 400 ° C and 800 ° C.

19. The method according to claim 17 or 18, characterized in that after the process step c) the epitaxial substrate (7) is removed.

20. A method for producing a radiation-emitting semiconductor body (1) according to one of claims 11 to 13 or according to one of claims 14 to 16 with reference to one of claims 11 to 13, characterized by the steps: a) producing and providing a self-supporting Epitaxy substrate (11) which consists essentially of AlGaAs and has an Al content at which AlGaAs is transparent to the radiation generated, b) growth of the layer sequence (2) on the epitaxial substrate by means of organometallic gas phase epitaxy or molecular beam epitaxy at a second process temperature ( Area?) .

21. The method according to claim 20, characterized in that the epitaxial substrate is produced by means of a vertical gradient freeze (VGF) method.

22. A method for producing a substrate (3) for growing a radiation-emitting semiconductor body, characterized by the steps: a) providing an epitaxial substrate (7), b) growing an AlGaAs layer (4, 5, 6) onto the epitaxial substrate (7) by means of liquid phase epitaxy. , the Al content in the AlGaAs layer decreasing with increasing growth thickness and the thickness of the AlGaAs layer being selected such that the Al content is not or only up to a thickness of approx. 30 nm below the transparent layer. limit for the radiation generated in the intended radiation-emitting structure; c) repeating step b) until the desired thickness of the substrate, consisting of AlGaAs layers (4, 5, 6), is reached.

23. Substrate (3) for growing a radiation-emitting semiconductor body, that means that it has one or a plurality of successive ones

AlGaAs layers (4,5,6), which are produced by means of liquid phase epitaxy or a similar method, which on average have an Al content in which AlGaAs is transparent to radiation generated in the radiation-emitting semiconductor body, and in which each AlGaAs layer, starting from a side facing a first main surface of the substrate (3) towards a side facing a second main surface of the substrate (3) opposite the first main surface, has a decreasing Al content, the Al content not in it or only up to a thickness of approx. 30 nm below the transparency limit for the radiation generated.