P. D. Wright

Pulsed room‐temperature operation of In1−xGaxP1−zAsz double heterojunction lasers at high energy (6470 Å, 1.916 eV)

Pulsed room‐temperature operation of LPE In1−xGaxP1−zAsz double heterojunction (DH) laser diodes at short wavelength is described (Jth≲2×104 A/cm2, λ∼6470 A, heterobarrier ΔE∼137 meV). The differential quantum efficiency of these diodes is ηext∼5%, and is considered to be low because of large diode size, thick active region, probably some layer mismatch and growth defects, and relatively poor heat sinking. The temperature dependence of threshold current density (Jth∼J0 expT/T0, T0∼74 °K) is presented in the range 77–300 °K and is compared with similar diodes having smaller heterobarriers and which, as expected, exhibit poorer performance (smaller T0).

Yellow In1−xGaxP1−zAsz double‐heterojunction lasers

Improved yellow‐spectrum double‐heterojunction In1−xGaxP1−zAsz laser diodes constructed by LPE on VPE GaAs1−yPy substrates are described. The lattice‐matched LPE quaternary alloy growth process is outlined, as well as the need for complete melt removal between the growth of each heterojunction layer, which is more difficult for In‐rich melts than for Ga‐rich melts when lattice match is a problem. Over two times lower threshold current densities are demonstrated (Jth?3.6×103 A/cm2, λ?5920 A, 77 °K) than for the first reported diodes of this type. The temperature dependence of laser threshold current density is presented in the range 4.2–200 °K. The threshold current density can be approximated as Jth∝exp(T/T0) with T0?52 °K in the range 50–175 °K, which compares well with red‐orange AlGaAs double heterojunctions (T0?42 °K) having greater heterobarriers. Laser operation in the yellow‐orange portion of the visible spectrum at ∼200 °K is demonstrated. These results on thick (1.5 μm) active layer diodes, havin...

Low‐threshold LPE In1−x′Gax′P1−z′ Asz′/In1−xGaxP1−zAsz/In1− x′ Gax′P1−z′Asz′ yellow double‐heterojunction laser diodes (J<104 A/cm2, λ∼5850 Å, 77 °K)

Liquid phase epitaxial (LPE) In1−x′Gax′P1−z′ Asz′/In1−xGaxP1−zAsz/In1− x′ Gax′P1−z′Asz′ (x′∼0.66, z′∼0.005; x∼0.71, z∼0.10) double‐heterojunction laser diodes that operate in the yellow at relatively low current densities (J<104 A/cm2, λ∼5850 A, 77 °K) are reported. The lattice‐matched LPE quaternary growth process, employing GaAs1−yPy substrates, and the double‐heterojunction laser diode properties are described.

Multiple liquid phase epitaxy of In1−xGaxP1−zAsz double‐heterojunction lasers: The problem of lattice matching

Multiple liquid phase epitaxy of In1−xGaxP1−z Asz‐InP double heterojunctions, from a single set of In‐rich melts, is demonstrated, and is shown to be a useful technique for the study of the problem of lattice matching at heterojunction interfaces and for growing large numbers of low‐threshold (’’defect‐free’’) DH laser wafers (λ∼1 μm).

Planar Zn diffusion in InP

Abstract A procedure for achieving well-behaved planar Zn diffusion to a controllable depth in n -type InP is described. The dilute-Zn diffusion, which utilizes a Zn+Ga+P source (in an evacuated ampoule), is performed in the temperature range 650–700°C. The low diffusion temperatures employed assure that any previous junctions that might be prepared, such as LPE heterojunctions, are not affected by the diffusion process. The masking afforded by Si 3 N 4 and partial “masking,” or attenuation, afforded by SiO 2 on InP are demonstrated. The results obtained suggest that dilute-Zn diffusion in InP, with a significant P over-pressure, favors a substitutional diffusion mechanism that probably follows a complementary error function distribution.

Liquid phase epitaxial In 1-x Ga x P 1-z As z /GaAs 1-y P y heterojunction lasers

The growth and laser properties of In 1-x Ga x P 1-z As z / GaAs 1-y P y single heterojunction laser diodes are described. High-quality p-type In 1-x Ga x P 1-z As z layers are grown by liquid phase epitaxy (LPE) on n-type VPE GaAs 1-y P y substrates of composition y = 0.32 - 0.40 . Laser operation (77 K) of these quaternary-ternary heterojunctions is demonstrated at shorter wavelengths ( J_{th} \lsim 6.2 \times 10^{4} A/cm2) than comparable GaAs 1-y P y homojunctions. The increase observed in threshold current ( 5x ) between y = 0.38 and y = 0.40 GaAs 1-y P y substrates is attributed to the usual effect of E X approaching E_{\Gamma} near the direct-indirect transition. From the well-defined cavity mode structure observed on these hetero-junctions, data are obtained at relatively high energy on the index dispersion quantity {n - \lambda(dn/d\lambda)} , which increases monotonically with photon energy and provides a reference for the distinctly different behavior observed on N-doped GaAs 1-y P y (h_{\nu} \sim E_{\Gamma} \sim E_{N}) .

Homogeneous or inhomogeneous line broadening in a semiconductor laser: Observations on In1−xGaxP1−zAsz double heterojunctions in an external grating cavity

In1−xGaxP1−zAsz double heterojunctions (77 °K, yellow) are shown to exhibit either (or both) homogeneous or inhomogeneous line broadening when operated as lasers in an external grating cavity. Just above threshold, inhomogeneous line broadening is observed over much of the recombination spectrum. Well above threshold (large gain), homogeneous line broadening is observed when the grating is tuned onto the cavity modes in the region of line center.

Defect‐ and phonon‐assisted tunneling in LPE In1−xGaxP1−zAsz DH laser diodes (λ∼1 μm)

Tunnel diode I‐V, dI/dV, and d2I/dV2 characteristics are used to examine defect effects and phonon energies in In1−xGaxP1−zAsz double‐heterojunction lasers (λ‐1.1 μm) grown by liquid‐phase epitaxy on InP substrates. Similar to the usual conductance minimum observed at zero bias, a conductance minimum in the dI/dV characteristics is observed at small forward bias (40⩽V⩽60 meV) and is identified as two‐step tunneling (via defects) to Zn‐acceptor states on the p‐type side of the junction. An increase in the conductance is observed below the region of carrier injection and is attributed to tunneling from residual acceptor states on the n‐type side of the junction. Fine structure in the dI/dV and d2I/dV2 characteristics permits the identification of optical phonon energies at two In1−xGaxP1−zAsz compositions (x=0.12, z=0.26; x=0.16, z=0.35) and in this region indicates two‐mode behavior for the quaternary alloy.

Near-infrared In 1-x Ga x P 1-z As z double-heterojunction lasers: Constant-temperature LPE growth and operation in an external-grating cavity

InP-In 1-x Ga x P 1-z As z -InP ( x \sim 0.08, z \sim 0.17 ) double-heterojuncfion (DH) lasers emitting at \lambda \sim 1.0 \mu m (77 K) have been fabricated by constant-temperature liquid-phase epitaxy (LPE). The crystal-growth process is described and compared to previous work on visible spectrum ( \lambda \sim 6000 -A) In 1-x Ga x P 1-z As z double-heterojunction lasers. Emission spectra are presented for the near-infrared quaternary DH lasers. In particular, the observation of cavity oscillations in the low-level spontaneous-emission spectra allows the determination of the index dispersion quantity over a wide wavelength range. Finally, these In 1-x Ga x P 1-z As z DH lasers are operated in an external-grating cavity. Such operation permits tunable, narrow-linewidth laser emission and provides information concerning radiative-recombination processes. Comparisons are made to earlier work on external-grating operation of visible-spectrum ( \lambda \sim 6000 -A) In 1-x Ga x P 1-z As z DH lasers.

Heterojunction laser operation of N‐free and N‐doped GaAs1−yPy (y=0.42–0.43, λ∼6200 Å, 77 °K) near the direct‐indirect transition (y∼yc?0.46)

The successful LPE growth of In1−xGaxP1−zAsz/ GaAs1−yPy single heterojunctions on VPE substrates makes possible the study of stimulated emission in N‐free and N‐doped GaAs1−yPy in a region (y=0.42–0.43) much closer to the direct‐indirect transition (y≡yc=0.46, 77 °K) than previously. Laser operation in N‐free GaAs1−yPy on the Γ‐Zn (EΓ‐EZn) recombination transition has been achieved at energies as high as 2.00 eV (λ=6200 A), and some line narrowing has been observed at energies as high as 2.01 eV (λ=6170 A, y=0.43). In contrast to diodes made on lower composition substrates, the diodes of this work do not change their threshold current densities in the range 77–4.2 °K, indicating that laser operation occurs on direct transitions lying within ∼kT of the indirect donor states (Te) associated with the X conduction‐band minima. From EΓ+kT∼EX−Ed (y=0.42–0.43), the depth of indirect Te donor states in GaAs1−yPy is estimated to fall in the range Ed=22–32 meV. Nitrogen doping in these laser diodes increases the th...