JPH0311691A - Monolithic high-density array of independently addressable offset semiconductor laser source for double beam or multiple beam polygon mirror ros printer - Google Patents

Abstract

PURPOSE: To make interlaced scanning unnecessary and simplify the structure of optical system, by making it possible to simultaneously write two adjacent scanning lines on an image bearing surface, by the offset of laser elements. CONSTITUTION: Active regions 16 which generate and transmit light waves in the state of laser operation are contained in a plurality of semiconductor layers formed on a substratum 12. Impurity induction disordering penetrates the active regions 16, and regions being adjacent in the lateral direction turn to disordered alloy regions 28. The regions 28 are formed to have a depth which can optically isolate laser elements 13A, 138 so as to evade the phase- locked state. Barriers 25A-25C are formed to stretch inside an array, and made adjacent to each other, while electric and thermal crosstalk to the independent operation of the elements 13A, 138 is restrained to a minimum. Isolated pumping contacts 22 and 24 are formed in order to make it possible to simultaneously write two adjacent scanning lines on an image bearing surface. Thereby interlaced scanning is made unnecessary, and the structure of optical system can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides impurity-induced disordering (impurity 1
Semiconductor lasers fabricated after device growth using reduced disordering (110), particularly multi-emitter semiconductor lasers with minimal electrical and thermal crosstalk and high efficiency for use in high speed rusk output scanners (ROS) and laser printers. It relates to array manufacturing and construction.

The ability to produce closely spaced but independently addressable laser sources is important in many applications such as optical disk technology, laser printing, optical interconnects, and fiber optic communications. To simplify the structure of the optical system, it is often desirable to have the laser elements of the laser array as close together as possible. For optical connections, especially when the spacing between the laser elements is only a few microns, it is highly desirable to provide the device with the p-side up in order to simplify the separation of the electrical connections with the laser device. However, this limits the device's ability to achieve CW operation. Previous attempts have been made to individually connect the laser elements of such devices, but these devices are not capable of CW operation. Also, poor light and carrier confinement cannot prevent coupling and phase locking between laser sources.

Although acceptable 6W performance has been achieved with p-side-up etched and regrown buried heterostructure lasers, reliability and yield are key challenges in manufacturing high-density laser arrays with this technology. It has become.

Generally m-v group material composition, e.g. GaAs/Ga8]
The As single hemitter laser has a designed high refractive index cavity formed between laterally adjacent regions of relatively low refractive index. Such optical cavities can be created by non-planar growth mechanisms such as channels or mesas formed in the laser substrate or by holoniacs.
yak) is known to be formed by impurity-induced disordering (+IO) as shown in US Pat. No. 4,378,255. According to this patent, semiconductor structures containing quantum well features, such as multiple quantum wells, undergo compositional disordering by diffusion of impurities. Diffusion of impurities into spatially separated regions of the quantum well feature mixes A1 and Ga in the well feature, so that the average refractive index of the diffusely disordered region of these layers is lower than in undisordered regions, including central regions between spatially separated regions. This central region can be used as an optical waveguiding cavity for laser generation and/or pre-blanking.

Silicon impurity-induced disordering (Si-110) technology provides power conversion rates of 50% at power levels of several milliwatts.
It has been shown that it is possible to fabricate buried heterostructure lasers with low thresholds on the order of %. This high level of performance allows
These types of devices can be mounted p-side up for CW operation.

In addition, this type of laser array with a narrow center-to-center distance of 4 μm and a single-contact address electrode is 5i-110
It has been found that a high refractive index optical waveguiding mechanism through a 2000 µm nanotube results in high uniformity and no phase-locked operation.

A major problem with semiconductor lasers is the separation of monolithic laser sources close enough so that two adjacent scan lines can be written simultaneously. As a result, most systems attempting to use semiconductor multiple emitter sources utilize interlaced scanning systems that simultaneously write non-adjacent scan lines at the image-bearing surface, e.g. every third or fourth scan line. are doing. When utilizing non-adjacent scan lines, print quality is greatly influenced by the temporal stability of the scanning system and photoreceptor speed, as scan lines that are actually adjacent are written in separate real-time frames. Therefore, this is not a suitable solution. Therefore, device vibrations originating from various mechanical components have a significant negative impact on print quality. Also, the interlacing devices used to write scan lines require data buffers, which further complicates the drive electronics, and the complexity increases rapidly as the number of independent write sources increases.

The primary object of the present invention is to use +10 in providing a dense array of independently addressable semiconductor laser sources that can be used in particular for ROS and laser printing;
Sufficient spatial space to allow at least two adjacent scan lines to be written simultaneously without the need for complex optics to effect beam transformation onto the image-bearing surface, especially in interlaced scan, data buffer and ROS environments. Marry by providing two writing sources at a distance.

According to the invention, a double beam or multibeam polygon R
Monolithic high-density array of independently addressable offset semiconductor laser sources for OS printers or devices
Minimizes electrical and thermal interactions or crosstalk between independently addressed laser elements without phase locking and interfering with their independent operation.
They can be arranged with closer center-to-center distances than was previously possible.

An independently addressable semiconductor laser array according to the present invention comprises a plurality of semiconductor layers deposited on a substrate forming at least two laser elements spatially separated within an optical cavity with at least one offset. and the layers include active regions that generate and propagate light waves during lasing conditions. Impurity-induced disordering (110) is performed in each region through the active region, thereby disordering the spatially separated regions laterally adjacent to and between the optical cavities. Make sure it is in the alloy area. These disordered regions are deep enough to optically isolate the laser element from becoming phase-locked. Additionally, barriers are formed between the laser elements and extend into the array a distance sufficient to electrically isolate the individual laser elements. The combination of disordered alloy regions and barriers allows laser elements to be brought into close proximity while minimizing electrical and thermal crosstalk for independent operation of the individual laser elements. The distance between the centers of the laser elements is
3-10 μm can be achieved without undesirable electrical, optical and thermal crosstalk. The cross-connection resistance between the laser elements can be, for example, about 15 MΩ, and the capacitance can be 0.2 pF or less. Means are provided for narrowing the parasitic junction in the laser device, the depth of which is limited to the depth of the electrical isolation barrier. The independently addressable semiconductor laser array of the present invention has at least two laser emitters spatially separated, or staggered, by a sufficient distance to enable writing two adjacent scan lines on an image bearing surface simultaneously. This eliminates the need for interlaced scanning and the complex optics and beam alignment required for interlaced scanning. This offset moves the two emitters in the sasicle direction by half the beamwidth so that the beam is offset by an amount very close to that required for a non-interlaced scan line when scanning is done parallel to the plane of the laser. This can be achieved by forming the two parts to be shifted by a distance corresponding to . Minor error adjustments in the height of the resulting offset can be performed by slightly rotational adjustment of the laser array.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, advantages and details of the present invention will be better understood from the following description taken in conjunction with the accompanying drawings.

FIG. 1 shows a first embodiment of a monolithic high density array 10 of independently addressable semiconductor laser sources of the present invention. The array 10 includes a cladding layer 14 of n-Ga, -xAIxAs and an undoped or p-
type, doped or n-doped, relatively thin conventional double heterostructure (DH > active layer, or
Either a single quantum well of GaAs or Ga, -yAlyAs (where y is a very small number, x>y), or an alternating well layer of GaAs or Ga+-, AI, As and AlAs or Ga,-, , AI, -As (where x,
an active region 16 with a multi-quantum well structure consisting of corresponding barrier layers of y'> y) or a separate single or multi-quantum well structure in separate confined cavities;
p-Ga+-zAIJs (x, z, y'
y) and a p'' GaAs cap layer 20 are epitaxially deposited on an n-GaAS substrate 12. The epitaxial deposition can be performed by known MOCVD.

When implementing the invention, the light emitting points 17 of the individual facets
It is necessary that the multiple emitters of laser array E0, denoted by , be sufficiently close together but not operating in phase lock. This means that the two or more elements making up the laser array are sufficiently dense pixel arrays that are needed to obtain good printing resolution, as is the case with the light receptor surface of a printer, for example. Despite the high density required to focus on the image-bearing surface so that it can be formed, it is possible to make it independently addressable.

Typical layer thicknesses are, for example, 0.5 for the cladding layer 14.
~1.5 μm 1 active region 16 is, for example, 50 nm ~30 μm
0 nm thick conventional active layer or about 3 nm to 5 Q nm thick GaAs quantum wells and about 1 nm to 15 nm thick Ga+-Y Aly-As, where y'' is 0.1 to 1.
0) has a superlattice structure with a barrier layer. The cladding layer 18 has a thickness of 01 to 1.0 μm. The cap layer 20 has a thickness of 0.
The thickness is 1 to 1.5 μm. The actually formed array 10 consists of a 0.7 μm thick GaAs buffer layer (not shown) on an n-GaAs base material 12, a 0.7 μm thick n-GaAs buffer layer (not shown), and a 0.7 μm thick n-GaAs buffer layer (not shown).
Gao, aAlo, 2As buffer layer (not shown), 1
．． 4 μm thick n-Gao, 6A10.4AS cladding layer 14 and 56 nm thick multi-quantum active region 16
The four GaAs wells have three barrier layers of 0.9 μm thick GaO, 68LO, 4AS, and 1.4μm thick GaAs wells.
It is provided between a μm thick p-Gao, eAlo, 4AS cladding layer 18 and a 0.1 μm thick p-GaAs cap layer 20.

To form a multiple emitter array laser, in this example a dual beam emitter array laser, impurity induced disordering (+10) techniques, such as diffusion disordering or implantation/anneal disordering, are used.

It should be noted here that these forms of disorder are not limited to conventional ones such as impurities, but include disordering the crystal by diffusion, or damaging the crystal by implantation and then adding that damage to the crystal. The crystals are scaled up to high temperature annealing to form the desired disordered crystals.

To form a multi-emitter laser array 10, 5i3
A mask L 2 is formed on top of layer 20 with openings for performing the IID technique in each region of the laser structure. Optical cavities and current confinement for laser elements 13A and 13B are achieved by selectively diffusing high concentrations of eta-type impurities into regions exposed by the masking operation of the laser structure. For example, silicon can be selectively diffused in a semi-hermetic graphite boat containing a suitable diffusion source at temperatures above 800° C. for a sufficient period of time. This treatment method is generally carried out in a hydrogen stream. By diffusing silicon into the quantum well active region 16, GaAs-GaAlAs in the active region is
A1 and Ga are mixed to form the IID region 28 in FIG.
A GaAlAs alloy is produced with an average AlAs mole fraction given as .

Thin active layer of GaAs, or GaAs or Ga+-
In the case of a single quantum well layer of IyAs, Ga in the active layer and A1 of the adjacent Ga+zAI□As cladding layer 18 are mixed.

In the case of multiple quantum well structures, intermixing with Ga occurs primarily between the well and barrier layers, but extends to one or more of the alloy cladding layers 14 and 18. The silicon diffusion is carried out at, for example, 850° C. and maintained for a sufficient period of time, for example several hours, to penetrate through active region 16 to point 29. In the example above, disordered region 28 has a depth of about 1
．． The width of 5 μm is approximately 8 μm. The center-to-center distance of the laser elements or laser sources 13 is approximately 10 μm, and the active region 1
The width of 6A is approximately 2 μm.

Following the formation of region 28, a p-type zinc diffusion 21 is formed across the surface of the structure to a depth indicated at 23.

This provides good ohmic contact and reduces the resistance of the laser element 13. Next, two electrically insulating barriers are selectively formed as shown at 25A, 25B and 25C in FIG. These barriers 25 prevent zinc diffusion 2 by e.g. proton implantation.
1 to form a current pumping channel 32 with a width of approximately 4-5 μm.

The implants 25B between the laser elements 13 provide electrical isolation between these laser sources or emitters to a level that allows independently modulated laser operation without electrical or thermal crosstalk. This is an important part. The depth of the barrier 25 may be, for example, 0.3 to 0.5 μm.

Standard photo printing lift-off technology uses laser element 13A
and Cr-Au forming separate pumping contacts 22 and 24 for separately pumping 13B.
patterned metallization. The connection is completed by attaching the metal contacts 26 to the bottom surface of the substrate 12.

Silicon diffusion region array 28 functions to at least partially disorder the quantum well structure within active region 16 . In the planar laser structure of the active region 16 formed in this way, the guide region with a high refractive index is connected to the active region 16.
remains within the undisordered part of.

The region of the laser element 13 has a higher refractive index than the disordered region 28 adjacent to the active region 16, and therefore has a high waveguide function. Additionally, as shown in FIG. 2, IIDn+ region 28 forms a p-n junction 19 at the boundary of high aluminum cladding layer 14, which
The turn-on voltage is higher than that of the junction 15.

Because the width of the material band gap at junction 19 is significantly wider than at the active region junction, the current flowing at junction 19 at a given junction voltage is significantly lower than at laser junction 15. Therefore, the leakage current flowing through the high aluminum junction 19 is a small fraction of the total current flowing through the laser element, and in particular the barrier 25A, which damages and electrically isolates the area of the junction so that it does not function as a conductor. 25B and 2
Since the width of the joint portion 19 is extremely narrow due to the formation of 5C, the performance of the device is not significantly reduced.

An important feature of the invention is that each emitter is
The objective is to eliminate or reduce to an acceptable level crosstalk or interference in high speed modulation and CW optical oscillation in the operation of closely spaced dual beam lasers 10 with a spacing of 0 μm, especially 3-6 μm. For printing applications, when the optical output of one laser element changes in response to the modulation of the other, for example, when the optical output of one laser element increases or decreases due to the rise or fall of the modulation of the other laser element, It is necessary to prevent modulation crosstalk from appearing since the quality and resolution of the imaging on the printer's light receptor surface is affected. In addition, oscillation crosstalk of one laser element due to simultaneous Cl11 oscillation with the other laser,
In other words, a change in intensity - for boat fishing, a change in the direction of decrease in intensity is acceptable if the decrease in light intensity is small, for example 2% or less. Photoreceptor images produced by 800spi ROS printers have smaller tolerances for light intensity variations. In a laser printer, it is desirable to minimize the difference in oscillation threshold current ΔTth between two such laser elements 13A and 13B, which will soon increase the CIV oscillation of the other laser as the difference in current increases. This is because the light intensity of one of the oscillating lasers decreases.

FIG. 3 shows an equivalent circuit of the laser 10.

The measured value of the coupling resistance 33 between the laser elements 13A and 13B is, for example, 15 to 19 MΩ. The coupling capacitance 36 at IMHz AC is, for example, approximately 0.1 to 0.2 pF.

Series resistances 34 and 35 of each laser element 13A and 13B are approximately 8Ω, respectively. The important thing here is that
It is this series resistance that determines the overall power conversion efficiency that can be achieved. While the optical output power has a linear correlation with the input current above the lasing threshold,
Since the resistive power loss P=12 R has a quadratic correlation with the input terminal to the laser element, at a sufficiently high input current the resistive loss ultimately dominates the optical output power. For this reason, series resistance becomes an important parameter when determining the performance specifications of a low threshold laser device. The use of thin lasing filaments to obtain low threshold currents often results in series resistances that are so high that the gains achieved in obtaining low threshold current devices are negated. . 45% obtained with laser 10
Its high power efficiency is largely due to its low series resistance of 8Ω. A cross-connect or coupling resistance of 15 MΩ is passed through the cap layer 20 to the emitter or laser element 1.
This is due to the high resistance of the proton implant extending to a depth of about 500 nm in the region between 3A and 13B, resulting in a cross-coupling capacitance of 0.2 pP.

A double stripe laser 10 manufactured by another method in which the emitters are placed close to each other with a center-to-center distance of 10 μm or less, for example, has a low value of cross resistance 33 and is reported to be as high as 1.4 Ω. High-speed modulation crosstalk is very large. That is, the forward voltage of one laser element increases when the other laser element is turned on above a threshold, and therefore the light intensity of that laser element decreases,
Furthermore, when the other laser element is turned on, the light intensity increases and the forward voltage decreases. For example, Y. Tokuda et al.'s paper "Dual wavelength emission from a twin-stripe single well laser"
Wavelength Emission From
a Twin 5tripe SingleQuant
um well La5er) J, Applied Physics Letters (Aflp) 1edPhysics Letters)
, Volume 51 (21), pp1664-1666°198
Please refer to the issue published on November 23, 2007. Thus, it is important to have a sufficiently high coupling resistance and a sufficiently low coupling capacitance to sufficiently suppress modulation and CW oscillation crosstalk to acceptable levels for photoreceptor printing applications. .

However, a peak change in the spike-like light intensity change is always seen when modulating one laser element relative to the other. 8
The tolerance for such a peak change in light intensity in a standard receiver image print at 00 spi is 2
This is about 4% of the light intensity that can turn on one pixel. Laser 10 with modulation of 5 MHz and pumping current of 17 mA
is approximately 1.7% of the total turn-on light intensity, which is sufficient. However, the ratio between cross-connected impedances 33 and 36 to series resistors 34 and 35 is sufficiently or significantly large that the current flowing through impedances 33 and 36 is negligible, such that CW or pulsed operation of one laser element It is clear that it is an important factor that the laser element be substantially unaffected by the operation of the other laser element.

Another type of crosstalk that must be considered in the case of independently addressable closely spaced laser elements in a laser array is thermal crosstalk. Heat generated from the operation of one laser element is thermally diffused to the other laser element, reducing its optical power output due to the increased operating temperature. Such thermal crosstalk can occur in either laser elements 13A and 1.
Compensation is difficult because the instantaneous power of 3B depends on the power output of the other laser element, which was previously operated in a different period. However, from experiments, the laser element 13A
Thermal crosstalk between and 13B has been found to be insignificant.

The laser array 40 of FIG. 4 is provided with an offset 41 for scanning adjacent lines on the image bearing surface, thereby providing interlaced scanning and appropriate beam conversion and modulation data to the image bearing surface in space 9. Additional associated optics and electronics shown in the interleaved scan lines can be omitted. The laser array 40 is
It is fabricated similarly to laser array 10, but with one or more steps 43 etched into substrate 42 before growth and two integral layers after all semiconductor layers of the structure have been evixtally deposited. The difference is that the height is calibrated to provide the desired amount of offset 41 needed between the laser emitters. The laser array 40 has n
-On top of the GaAs base material 42 n-Ga+-xAIxA
s outer cladding or buffer layer 44, n-Ga+-z
17. It is constructed by evictively adhering an IzAs cladding layer 50 and a cap layer 52 to the inner cladding layer 46 of ^S (where x > z), the active region 48, and pGa1-z.

After depositing the layers, IID regions 54 are formed as previously described. Following the formation of region 54, p-type diffusion 56
is formed at the surface of the structure to a depth indicated at 55 to provide good ohmic contact and reduce series resistance. An electronically insulating barrier 58 is then selectively formed deeper than the diffusion zone 56 by proton implantation to form a current pumping channel 60. The implant area between laser elements 62 is to a level that allows independently modulated laser operation without electrical or thermal crosstalk.
These emitters are electrically isolated.

Standard photo printing lift-off technology uses laser element 62A
and 62B are utilized to pattern the metallization of Cr-8U to form separate contacts 64 and 66 for separately pumping. The connection is completed by attaching metal contacts 68 to the bottom surface of substrate 42.

Actually, the distance between the centers of the laser elements 62 is 10 μm,
Beyond that, active regions 48A and 48B are approximately 2μ
Make it width m. Offset 41 is about 1 μm. In the case of a typical ROS, the ROS magnification is 50x, so
A 1 μm offset with a 10 μm center-to-center spacing is optically translated into a laser beam with a 50 μm center-to-center spacing at the image bearing surface and adjacent scan lines spaced approximately 150 μm apart. Approximate tilting of the laser array 40 to provide a scan line offset between emitters, as is required with the in-line double beam emitter of FIG. 1, is not required. In the case of FIG. 1, the laser 10 must be tilted slightly, for example 2 degrees, to maintain offset adjustment. However, experiments have shown that it is very difficult to maintain such a slightly rotational positional relationship for uniform scan line maintenance. By automatically applying the necessary offset corresponding to half the beam width, the laser array 40
When scanned parallel to the plane of emitters 48A and 48B, the beam can be automatically offset by an amount very close to that required for a non-interlaced scan line. Minor error adjustments in the height of the offset can be made by rotational adjustment of the laser 40, which is much easier to implement than the rotational adjustment required for the laser 10. This is illustrated in FIG. 5, where 70 indicates a packaged dual beam laser with emitters 72 and 74 offset by S, for example 1 μm. The reference point 76 is a point outside the package 70 for grading the rotational momentum about the origin of the X-Y axis to adjust for slight errors in the offset height S, i.e. S is Accurate correction can be made by finely adjusting Δβ.

Although the illustrated embodiment of the present invention is an offset dual beam laser, the present invention may It is clear that it can be extended to multiple beam lasers such as heavy spot lasers. In such a structure,
- An offset of 1 μm is included between several emitters so that several spatially adjacent scan lines of the imaging plane, e.g. a light receptor or printer surface, can be scanned simultaneously.

Although the invention has been described in terms of several specific embodiments, it will be obvious that various modifications may be made from the above description. Accordingly, the present invention includes all such modifications that do not depart from the scope of the claims appended hereto.

[Brief explanation of the drawing]

1 is a schematic side view of a semiconductor laser array having two laser elements, illustrating the invention in detail; FIG.
The figure is an enlarged view of one of the laser elements shown in FIG.
FIG. 3 is an equivalent circuit diagram of the laser array shown in FIG. 1, FIG. 4 is a side view of the offset double beam semiconductor laser array of the present invention, and FIG. 5 is a slight rotational adjustment of the package in a ROS system. FIG. 2 is a schematic side view of a dual beam laser package for explaining. 10 near array 12; base material 13A 138: laser element 14: cladding layer 15
: pn junction 16.16A : active region 17
: Luminous point 18: Cladding layer 19: pn
Joint part 20: Cap layer 21: Diffusion part
22, 24: Contact 25A 25B, 25C: Barrier
26: Contact 28: ID area 29: Point 32: Channel 33: Coupling resistance 34.35:
Series resistance 40: Laser array 41: Offset 42: Base material 44; Buffer layer 46: Cladding layer 4 48, 488, 488: Active region 52; Cap layer 56: P-type diffusion 60: Channel 64. 66: Contact 70 ; dual beam laser 76: reference point 50: cladding layer 54: 110 region 5B: barrier 62A, 628: laser element 68; metal contact 72.74: emitter

Claims (1)

[Claims] 1. An independently addressable semiconductor laser array that generates multiple beams to scan the image-bearing surface of a ROS printer, the array comprising at least two laser elements in spatially separated optical cavities that are sagittally spaced apart from each other in beam width. a plurality of semiconducting layers offset by half, the layers including active regions that generate and propagate light waves during laser operation; and the spatially separated optical cavities. fundamental constituents of the active region and at least one adjacent semiconductor layer are at least partially diffused and disordered by being directed through the active region into laterally adjacent regions and regions therebetween; an impurity forming an alloy region, the disordered region having a depth sufficient to optically isolate the laser element from becoming phase-locked;
barrier means formed between the laser elements and extending into the array a sufficient distance to sufficiently electrically isolate the laser elements; and means for independently pumping the laser elements; An independently addressable semiconductor laser array that eliminates the need for interlace scanning by allowing two adjacent scan lines to be simultaneously written on the image bearing surface by offsetting laser elements.