DE19945128A1 - Vertical resonance laser diode has a protective layer made of a hermetically sealed dielectric, especially silicon nitride applied to the whole region of a Bragg reflector layer sequence - Google Patents

Abstract

A protective layer (9) made of a hermetically sealed dielectric, especially Si3N4 is applied to the whole region of the Bragg reflector layer sequence (4). Vertical resonance laser diode comprises an active layer sequence (3) for producing laser radiation between a first Bragg reflector layer sequence (2) and a second Bragg reflector layer sequence (4), each having a number of mirror pairs (22, 44). Both Bragg reflector layer sequences form a laser resonator. Both Bragg reflector layer sequences and the active layer sequences are arranged between a first and a second electrical contact layer (7, 8).One (4) of the layer sequences is partially permeable for the laser radiation produced in the active layer sequence. The electrical contact layer has a opening (7A) for light. A protective layer (9) made of a hermetically sealed dielectric, especially Si3N4 is applied to the whole region of the Bragg reflector layer sequence (4). Preferred Features: The protective layer covers the edge region of the opening formed by the electrical contact layer. The protective layer is applied by plasma-supported chemical gas phase deposition or radio frequency sputtering.

Description

The invention relates to a vertical resonator laser diode the preamble of claim 1.

Vertical resonator laser diodes (VCSELs) are said to be in packaging are used that are not herme to the environment table are insulated. Obtain such "open" structures increasing interest due to their low manufacturing costs and their space-saving structure. When packing for Components to be used, however, must be packaging VCSELs determined in their reliability data meet typical requirements. Especially with the location tion in a humid atmosphere at an elevated temperature (Moisture-heat storage), at z. B. a temperature of 85 ° C. and 85 ° C humidity, VCSELs have so far shown an instabi les behavior.

Accordingly, the present invention has the object reason to create a vertical resonator laser diode that sufficiently stable against environmental influences such as heat or moisture.

This object is achieved by the features of patent claim 1 solved.

In the invention to be described here, a protective layer of a hermetically sealed dielectric, in particular made of Si ₃ N ₄ , is arranged over the entire area of the partially permeable Bragg reflector layer sequence of the vertical resonator laser diode that is exposed in the light exit opening. It is advantageous if the protective layer additionally covers the edge area of the light exit opening formed by the electrical contact layer over its entire circumference. The protective layer can advantageously be applied by plasma-assisted chemical vapor deposition (PECVD) or by radio frequency (RF) sputtering.

In the following the invention is based on a single embodiment example explained in more detail. Show it:

Fig. 1 shows the epitaxial layer structure of a erfindungsge MAESSEN vertical resonator laser diode;

Fig. 2 shows the slope as a function of the storage time of VCSELs without (A) and with a protective layer made of SiN (B).

The vertical resonator laser diode (VCSEL) shown in FIG. 1 is applied to a GaAs substrate 6 . On the GaAs substrate 6 there is a first, lower Bragg reflector layer sequence 2 , which is made up of individual identical mirror pairs 22 . The mirror pairs each consist of two AlGaAs layers of different aluminum concentrations. In the same way, a second, upper Bragg-Re reflector layer sequence 4 is constructed from corresponding mirror pairs. An active layer sequence 3 is embedded between the lower and the upper Bragg reflector layer sequence. In the illustrated embodiment, the emission wavelength of the laser diode is 850 nm. On the upper surface of the laser diode is a first metallization layer 7 , which is used for the electrical connection of the p-doped side of the laser diode. The first metallization layer 7 has a central light passage opening 7 A for the passage of the laser radiation. The n-doped side of the diode is usually electrically connected via a second metallization layer 8 contacted on the substrate 6 .

In the exemplary embodiment, the upper Bragg reflector layer sequence 4 contains a pair of mirrors which contains a so-called current aperture 41 . The current aperture 41 ensures a lateral current limitation and thus defines the actual active light-emitting surface in the active layer sequence 3 . The current flow is limited to the opening area of the Stromaper tur 41 . The light-emitting surface is thus directly below this opening area in the active layer sequence 3 . The current aperture 41 can be produced in a known manner by partial oxidation of the AlGaAs layers of the mirror pair in question or by ion or proton implantation.

The upper Bragg reflector layer sequence 4 of the laser diode is structured in the form of a mesa structure above the active layer 3 . The mesa-shaped upper Bragg reflector layer sequence 4 is laterally enclosed by a suitable passivation layer 11 .

In the area of the light passage opening 7 A, a protective layer 9 made of Si ₃ N _{4 is} applied to the upper Bragg reflector layer sequence 4 , through which the exposed surface of the Bragg reflector layer sequence 4 can be passivated and protected against the effects of heat and moisture. The protective layer 9 is applied 7 A in the entire region of the light passage opening and overlaps the by the electrical con tact layer 7 edge formed of the light passage opening 7 A over its entire circumference, so that the exposed Oberflä surface of the Bragg reflector layer sequence 4 hermetically ge genüber the environment is complete. In the edge region, the protective layer 9 thus has an elevation which corresponds in thickness to the thickness of the electrical contact layer 7 .

The protective layer 9 may be applied by means disposed at a small distance from the laser diode mask which has an opening that is slightly larger on all sides than the light passage opening 7 A. As a result, the overlap of the edge region with the protective layer 9 is made possible. It is also possible to apply the protective layer over the entire surface with a subsequent masked etching for structuring.

The PECVD or RF sputtering technology creates a tight seal Layer that damages the laser due to humidity prevents a gap-free seal over the ge entire aperture window area is reached. The important thing here is the electrically insulating property of the protective layer, the in this way the formation of a galvanic element between the metallic contact layer and the semiconductor of the Light exit window prevented.

In the first experiments, protective layers made of Si ₃ N ₄ showed clear advantages over, for example, Al ₂ O ₃ , which was applied by ion beam sputtering and with which a satisfactory hermetically sealed passivation of the laser diodes could not be achieved.

The positive effect of the protective layer made of Si ₃ N ₄ is illustrated in FIG. 2. In FIG. 2, the steepness of VCSELs as a function of storage time in a damp is (humidity 85%) atmosphere shown at elevated temperature (85 ° C). The slopes of a total of 15 samples are plotted. These VCSEL components have a protective layer over the aperture window, but not a protective layer made of PECVD-Si ₃ N ₄ according to the present invention, but a protective layer made of Al ₂ O ₃ . Individual VCSELs in FIG. 2A show clear fluctuations in the slope, which is due to damage to the laser. The Al ₂ O ₃ deposited by ion beam sputter deposition does not appear to cause the desired hermetically sealed passivation. With these VCSEL components, edge gaps of the passivation layer on the contact ring probably occur.

In contrast, the slope curves of a total of 15 VCSEL components are plotted over the storage time in FIG. 2B. These VCSEL components were provided with a Si ₃ N ₄ passivation layer. None of the steepness curves plotted in FIG. 2B shows a significant change in the steepness after a storage time of 2000 hours. Thus, all VCSELs whose steepness curves are plotted in FIG. 2B show very stable behavior when stored in a warm, humid atmosphere. This positive passivation effect has also been demonstrated in numerous other tests.

Reference list

2nd

first Bragg reflector layer sequence

3rd

active layer sequence

4th

second Bragg reflector layer sequence

6

Substrate

7

first metallization layer

7

A light passage opening

8th

second metallization layer

9

Protective layer

11

Passivation layer

22

Bragg reflector layer sequence

41

Current aperture

Claims (4)

1. Vertical resonator laser diode in which

• - An active layer sequence ( 3 ) for generating laser radiation is arranged between a first Bragg reflector layer sequence ( 2 ) and a second Bragg reflector layer sequence ( 4 ), each of which has a plurality of mirror pairs ( 22 , 44 ) is
• the two Bragg reflector layer sequences ( 2 , 4 ) form a laser resonator,
• the two Bragg reflector layer sequences ( 2 , 4 ) and the active layer sequence ( 3 ) are arranged between a first ( 7 ) and a second electrical contact layer ( 8 ),
• one ( 4 ) of the two or both Bragg reflector layers follow ( 2 , 4 ) is partially transparent to the laser radiation generated in the active layer sequence ( 3 ),
• - The first electrical contact layer ( 7 ) has a light outlet opening ( 7 A),

characterized in that

• - On the entire area in the light exit opening ( 7 A) exposed partially transparent Bragg reflector layer sequence ( 4 ) a protective layer ( 9 ) made of a hermetically sealed dielectric, in particular of Si ₃ N ₄ , is brought up.

2. Vertical resonator laser diode according to claim 1, characterized in that

• - The protective layer ( 9 ) through the electrical contact layer ( 7 ) formed edge area of the light exit opening ( 7 A) covers its entire circumference.

3. vertical resonator laser diode according to claim 1 or 2, characterized in that   - The protective layer ( 9 ) is applied by plasma-assisted chemical vapor deposition (PECVD) or by radio frequency (RF) sputtering.