Method forming surface emitting diode laser
AssigneeMassachusetts Institute of Technology
InventorsZong-Long Liau, James N. Walpole
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Abstract
A method and apparatus for forming a monolithic surface emitting laser diode array by providing vertical partly light transmissive mirror surfaces opposite parabolic light reflective mirror surfaces formed adjacent the active buried layer of a heterostructure diode laser. The mirror surfaces are preferably formed using a mass-transport heating process. Other mirror shapes may be formed in accordance with the invention.
Claims25
The method of forming a collimating element on a semiconductor surface comprising the steps of:
- (a) forming layers of semiconductor material on a substrate;
- (b) selectively etching the semiconductor layers to form a surface profile approximating the desired profile of the collimating element;
- (c) smoothing the surface to the shape of the desired profile by a heat treatment without etching.
The method of forming an array of surface emitting laser semiconductor devices comprising the steps of:
- (a) making a plurality of adjacent mesa structures on a substrate by:
- (i) forming a substrate;
- (ii) forming a first layer of semiconductor material over said substrate;
- (iii) forming a second layer of semiconductor material on the first layer;
- (iv) forming a first coating over a portion of said second layer;
- (b) removing a plurality of portions of said second layer on two adjacent sides of said protective coating down to the top surface of said first layer;
- (c) removing a plurality of portions of said first layer underlying adjacent sides of said second layer so as to produce undercut areas beneath the remaining second layer with volumes of first layers therebetween, said volumes of first layer having top, bottom and four side walls, with two adjacent side walls thereby being exposed to the atmosphere;
- and
- (d) heating the structure in a controlled environment to a temperature which causes the material in the regions of the undercut areas to travel into the undercut area and enclose the exposed side walls;
- (e) forming a second coating over said second layer with striped openings aligned with the portions of the first layer;
- and
- (f) removing portions of said second layer and first layer to expose first and second opposing walls;
- (g) forming in said mesa structure a partly light transmissive surface on the first opposing side wall and a light reflective parabolic surface adjacent said partly light transmissive surface on the second opposing wall.
The method of claim 14 wherein the parabolic surface is formed by removing a portion of the first and second layers on a side of the groove down to the substrate in the groove adjacent the side upon which the vertical mirror surface is to be formed to form a step-like profile in which the upper second layer is laterally recessed a distance "s" and wherein t.sub.2 is the thickness of the first layer and t.sub.1 is the thickness of the second layer with respect to the lower first layer then forming said step-like profile into a parabolic profile by subjecting the side to the heat treatment of step (b) of claim 23 and coating the profiled surface with a light reflective material.
The method of forming smooth vertical surfaces on a semiconductor device comprising the steps of:
- (a) making a body by:
- (i) forming a substrate;
- (ii) forming an active layer of semiconductor material on the substrate;
- (iii) forming a top layer on the active layer;
- and
- (iv) forming a coating over a portion of the top surface with openings provided where the smooth surfaces are to be located;
- (b) removing a portion of said top layer through said openings down to the top surface of the active layer;
- (c) removing the exposed portion of said active layer;
- (d) removing a portion of the substrate below said opening to form a nearly vertical cross-sectional profile below the openings;
- (e) removing the newly exposed active layer and producing a small undercut area beneath the remaining top layer;
- and
- (f) heating the body to cause the material in the top layer and substrate in the region of the undercut to fill in the undercut area and embed the exposed edge of the active layer and form a smooth mirror surface adjacent thereto.
The method of forming a smooth vertical surface on a heterostructure semiconductor laser device comprising the steps of:
- (a) making a heterostructure by:
- (i) forming a substrate;
- (ii) forming an active layer of quaternary III-V alloy semiconductor material on the substrate;
- (iii) forming a top layer of a binary compound semiconductor material on the active layer;
- and
- (iv) forming a coating over a portion of the top surface of the top layer with strip openings over the area where the smooth vertical surface is to be formed;
- (b) removing a portion of said top layer down to the top surface of the active layer by etching said binary compound but not said III-V alloy;
- (c) removing the exposed portion of said active layer by etching said quaternary III-V alloy but not said binary compound;
- (d) further removing portions of said substrate below the strip openings;
- (e) removing the newly exposed portion of the active layer;
- and
- (f) heating the heterostructure to cause the material in the region of the undercut area to migrate into the undercut area adjacent the active layer and form a smooth vertical surface adjacent said active layer.
The method of forming a surface light emitting quarternary III-V layer in a heterojunction device having alternate layers of quaternary III-V material and binary III-V material comprising the steps of:
- (a) selectively etching only the binary material until a mesa of binary material is formed over the layer of quaternary material and a surface of quaternary material is exposed on two sides of said mesa;
- (b) selectively etching only the quaternary material at the exposed surfaces until two undercut regions are formed under the mesa with a layer of quaternary material therebetween which is exposed on two sides;
- and
- (c) filling in the undercut region with binary material from said means sufficient to bury the exposed portion of said quaternary material;
- (d) selectively etching only the binary material on the means at an area where a smooth vertical surface is to be located to expose the two previously unexposed sides of the quaternary material;
- (e) selectively etching only the quaternary material thus exposed;
- (f) selectively etching the binary material in the space below and between the adjacent undercut regions;
- and
- (g) filling in the two adjacent undercut regions with binary material to bring the exposed portions of the quaternary material and form a smooth vertical surface adjacent one of the filled-in undercut regions and a parabolic surface adjacent the other.
A method of forming an array of surface emitting laser semiconductor devices comprising the steps of:
- (a) forming a plurality of edge emitting active laser devices on a monolithic substrate, said edge emitting active laser devices comprising p-n junctions formed of III-V material wherein laser light is emitted from said devices in a direction parallel to the plane of the p-n junction;
- and
- (b) forming a smooth partly light transmissive surface extending vertically normal to said plane and adjacent said junction;
- and
- (c) forming a parabolic light reflective surface opposite said normal surface to direct laser light emitted from said laser in a direction normal to said plane of the p-n junction.
Dependencies are inferred from the claim text.