The InGaAsP material epitaxially grown on the InP substrate is an important material for the fabrication of optoelectronic and microwave devices. The emission wavelength of InGaAsP / InP laser structure covers 1.0-1.7μm, covering two low-loss windows of 1.3μm and 1.55μm for silica fiber communication. Therefore, InGaAsP is widely used in the manufacture of important components in the field of optical fiber communication, such as modulators, lasers, detectors and so on. Epi wafer for laser diode of bulk 1.55um InGaAsP / InP grown from PAM-XIAMEN is as below, which includes very high doped and very thin tunnel junction layers:
1. Specifications of InGaAsP / InP Laser Wafer
No. 1 Laser Diode Epi Strcuture PAM170919-INGAASP
| Name | Material | Thickness [nm] | Doping | Strain | PL [nm] | Bandgap [eV] | Notes |
| Bonding Layer | InP | 10 | – | 1.34 | |||
| Supperlattice | InP | – | – | – | |||
| InxGa1-xAsyP1-y | – | – | 1110 | – | |||
| InP | – | – | – | ||||
| InxGa1-xAsyP1-y | – | – | 1110 | – | |||
| n-contact | InP | – | n = 1.5E18 | Si doped | – | ||
| SCL outer | InGaAsP | – | – | 1150+/-10 | – | ||
| SCL Inner | InGaAsP | 40 | – | 1250+/-10 | – | ||
| QW | InGaAsP (x3) | – | – | 1% compressive strain | 1550+/‐ 10 | – | |
| Barriers | InGaAsP (x2) | – | – | 0.3% tensile strain | 1250+/‐10 | – | |
| SCL Inner | InGaAsP | – | – | 1250+/-10 | 0.99 | ||
| SCL outer | InGaAsP | – | – | 1150+/-10 | – | ||
| InP | – | Zn doped | – | p-doped from graded 1E18 near InGaAlAs to undoped near InGaAsP | |||
| TJ layer | InGa(Al)As | 10 | – | p++ Zn-doped | – | ||
| TJ layer | InP | – | – | – | – | ||
| InP | – | – | – | – | n-doped from graded 1E18 near InP to undoped near InGaAsP | ||
| SCL outer | InGaAsP | – | – | 1150+/-10 | – | ||
| SCL Inner | InGaAsP | – | undoped | 1250+/-10 | – | ||
| QW | InGaAsP (x3) | 7 per well | – | – | 1550+/‐ 10 | – | |
| Barriers | InGaAsP (x2) | – | – | 0.3% tensile strain | 1250+/‐10 | – | |
| SCL Inner | InGaAsP | – | – | 1250+/-10 | – | ||
| SCL outer | InGaAsP | – | – | 1150+/-10 | – | ||
| p-cladding | InP | – | – | Zn doped | – | p-doped from graded 1E18 near InGaAs to undoped near QW | |
| p-contact | In.53Ga.47As | – | – | Zn doped | – | ||
| Buffer | InP | – | – | Zn doped | 1.34 | ||
| Substrate | InP | 350 um | n-doped |
Note:
For the structure of InGaAsP / InP herterjuntions, tunnel junction (TJ) layer should use 1250nm AlGaInAs or InGaAsP, the reason is that the long wavelength has smaller resistivity but if too long wavelength, it would be absorption for emission wavelength. 80nm InGaAsP cannot stop TJ impurity lons spreading to QW, here we suggest increasing thickness. Maybe 240nm InGaAsP can stop the diffusion, we should test it.
No. 2 InGaAsP / InP LD Epitaxial Structure PAM200420-INGAASP
| Layer | Material | Thickness | Notes |
| Layer 7 | InP | – | |
| Layer 6 | InGaAsP | – | |
| Layer 5 | InP | – | |
| Layer 4 | InGaAsP | – | |
| Layer 3 | InP | – | |
| Layer 2 | InGaAsP | – | emitting at 1575 nm |
| Layer 1 | InP | – | |
| Substrate: | InP, 3” |
No. 3 InGaAsP Heteroepitaxial on InP for LD PAM200708-INGAASP
| Epi Layer | Material | Thickness | Energy Gap |
| Layer 7 | InP | 100nm | |
| Layer 6c | InGaAsP | – | @1.25 eV |
| Layer 6b | InGaAsP | – | @0.85 eV |
| Layer 6a | InGaAsP | – | @1.25 eV |
| Layer 5 | InP | – | |
| Layer 4c | InGaAsP | 79 nm | @1.25 eV |
| Layer 4b | InGaAsP | – | @0.95 eV |
| Layer 4a | InGaAsP | – | @1.25 eV |
| Layer 3 | InP | – | |
| Layer 2c | InGaAsP | – | @1.25 eV |
| Layer 2b | InGaAsP | – | @0.85 eV |
| Layer 2a | InGaAsP | – | @1.25 eV |
| Layer 1 | InP | – | |
| Substrate | InP |
2. Growth of InGaAsP Layers
Compared with the ternary compound A1-xBxC, the band gap and lattice constant are determined by the same composition parameter x, while the quaternary compound A1-xBxCyD1-y can adjust the composition parameters x and y respectively to select different band gap and lattice constant. This adds variability and uncertainty to the epitaxial growth of the InGaAsP / InP double heterostructure (DH) wafer. For epitaxially grown quaternary materials, unless the device has special requirements, it is generally required to match the substrate lattice to avoid growth defects caused by lattice mismatch. For quaternary materials such as InxGa1-xAsyP1-y, because there are two composition ratios of III and V group elements, there can be countless combinations of x and y to meet the lattice matching requirements of the same substrate, which will bring great difficulties for adjustment and calibration of quaternary epitaxy parameters.
For the InGaAsP lattice matched to InP substrate, MBE technology is usually adopted. We can take advantage of the fact that the adhesion coefficient of group III elements is close to 100%, and the composition ratio between group III elements is relatively stable and repeatable. First, calibrate the composition distribution ratio of group III elements In and Ga, and then gradually adjust and calibrate the composition ratio between group V elements. Finally, the InGaAsP layers which are lattice matched with the InP substrate are obtained.
3. Chemical Etching of InGaAsP / InP Heterostructure
HBr:CH3COOH(H3PO4):K2Cr2O7 is a suitable solution for etching heteroepitaxial laser wafer grown with InGaAsP / InP MQW. This etching system can make the high quality etched surface without etch pits. For (001) InP, the etching rate changes from 0.1 to 10 um/min, which depends on the composition ration of solution or the normal line of K2Cr2O7 aqueous solution.
Mesa-like structures are formed on the (001) InP etched stripes parallel to the [110] and [110] directions. The etchant system etches InP and InGaAsP at nearly equal rates, thus providing ideal mesa-like structures with high-quality surfaces and good resist pattern definition. This solution does not corrode photoresist, making it attractive for kinds of device applications.
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