Название: VCSEL Industry
Автор: Babu Dayal Padullaparthi
Издательство: John Wiley & Sons Limited
Жанр: Техническая литература
isbn: 9781119782216
isbn:
Since 2020, VCSELs are manufactured on wafer diameters of 150 mm diameters and as previously described are compatible with high‐volume III–V semiconductor manufacturing processes. Many tens to hundreds of thousands of VCSELs can be fabricated on a single 150 mm wafer. With dramatic improvements in the epitaxial and fabrication processes, the device yields are routinely in excess of 90%. Details of wafer size and die counts will be given in Chapter 3. An example of fully processed VCSEL epitaxial wafer (so‐called deliverable‐wafer) is shown in Figure 1.12.
Figure 1.12 A fully processed VCSEL layer structure on 6″ (150 mm) GaAs substrate.
Source: Wafer photo by Jim A. Tatum, Dallas, Texas, USA. [copyright reserved].
1.3 VCSEL History and Development
During the four decades since the initial VCSEL conception in 1977, many hundreds of millions of VCSELs have been shipped from a large number of VCSEL manufacturers. Some of the more ubiquitous examples are laser printers, bar code scanners, computer mice, high‐speed data communications over fiber optic networks, 3D sensing in consumer and automotive electronics, night vision equipment, and many more industrial and consumer devices. It is not surprising to say that VCSELs have affected the life of nearly every person and household. With this background, we present a brief history of VCSELs from its birth to today’s use in many commercial products. We divide the time in five different periods to describe the generations of VCSEL development as shown in Figure 1.13 and detail the stages in the following paragraphs.
1.3.1 Stage I: Initial Concept and Invention
1.3.1.1 Stage Ia: Invention and Initial Demonstration
Now, what is this new surface‐emitting laser (SEL) or the vertical‐cavity surface‐emitting laser (VCSEL)? The structure is substantially different from conventional edge‐emitting lasers (EELs), i.e., the vertical cavity is formed by the surfaces of epitaxial layers, and light output is from one of the mirror surfaces orthogonal to the substrate as has been shown in Figure 1.13. It is recognized that one of the authors (Iga, from Tokyo Institute of Technology) invented VCSEL in 1977 [25–28] as shown in the inset of Figure 1.13. This new invention was coined VCSEL (vertical‐cavity surface‐emitting laser), following the naming of a “pixel,” which means any of the small discrete elements that together constitute an image (as on a television or digital screen). In the first stage, Ia, there were many technical challenges to overcome to realize this new device. The main challenges were the relatively low optical gain, overall mirror quality, and efficient current injection.
Figure 1.13 Stages of VCSEL development. The inset figure shows the sketch of VCSEL drawn by Kenichi Iga on March 22, 1977.
Source: Figure by K. Iga and B. D. Padullaparthi [copyright reserved by authors].
Figure 1.14 The first demonstration of a surface‐emitting laser.
Source: Figure by K. Iga [29] [copyright reserved by author].
The first device (prototype) was realized in 1979 using a GalnAsP‐InP material for the active region. The VCSEL operated at a 1300 nm wavelength [29]; a schematic cross section of the device is shown in Figure 1.14. This VCSEL used a double heterostructure with GaInAsP as an active layer, which was grown on an InP substrate. Light is emitted by injecting current from circular electrodes, and metal reflectors are formed above and below the substrate to form a resonator. This laser was driven by a pulsed current and was cooled to 77 K using liquid nitrogen. At 800 mA the device lased. When we looked at the light coming out of the device, it flashed rapidly at a certain current. It was possible to finally measure the spectrum, and it was much narrower than LEDs, which indicated laser oscillation. As mentioned above, the device was named surface‐emitting laser. The threshold was very high, more than 20 times that of a normal laser, and as such, the device was out of order immediately!
1.3.1.2 Stage Ib: First Room‐Temperature Continuous‐Wave Operation
In 1982, Iga and co‐workers made a VCSEL with 10 μm length cavity and confirmed the clear VCSEL oscillation [30]. In 1982, Iga’s group made a buried confinement VCSEL with a 6 mA threshold GaAs device using liquid phase epitaxy (LPE) [31]. A major breakthrough was the achievement of continuous‐wave (CW) operation at room temperature (RT) at 820 nm wavelength on GaAs substrate by Iga and Koyama (also from Tokyo Institute of Technology) in 1988 [32, 33]. The device structure is shown in Figure 1.15(a). The device was grown by metal organic chemical vapor deposition (MOCVD). With this achievement, global R&D of VCSELs has outperformed ordinary semiconductor lasers in the area of expertise. The concept of semiconductor DBR demonstration in 1988 [34] and the introduction of multi‐quantum wells into VCSEL [35] contributed to the improvement of VCSEL development in later years.
After this breakthrough from Tokyo Institute of Technology, continuous room‐temperature operation of the VCSEL, as shown in Figure 1.15(b), was also achieved by Jack Jewell and co‐workers at Bell Laboratories in 1989 [36, 37]. The concept of periodic gain or matched gain in quantum wells contributed to reduce the threshold by Larry Coldren and co‐workers [38, 39].
Figure 1.15 Initial VCSELs achieving room‐temperature continuous operation. (a) The VCSEL device that exhibited the first room‐temperature continuous‐wave operation by Koyama and Iga in 1988 [32].
Source: Copyright reserved by Fumio Koyama and Kenichi Iga
(b) A 2D micro‐post array by Jewell and Lee in 1989 [36, 37].
Source: Adapted from IEEE.
1.3.2 Stage‐II: Spread of Worldwide R&D
The second stage (1991–2000) covers the expansion of VCSEL research, the advancement in growth technology, and the emerging СКАЧАТЬ